Sustainability became a project variable. Now somebody has to set a tolerance on it

For thirty years, project management taught six variables. Time, cost, quality, scope, risk, benefits. Every method had its own diagram, but the underlying idea was the same: these are the things that can move, tolerance defines how far they may move without asking permission, and exceeding a tolerance triggers an escalation.

PRINCE2 7 added a seventh. Sustainability.

The full set of performance aspects is now benefits, cost, time, quality, scope, sustainability and risk. PeopleCert made a point of it at launch, and Henny Portman’s summary of the seventh edition — “human centric, AI/data analytics ready, tackles sustainability head on, more flexible than ever” — put it in the headline.

I have now sat through a number of conversations about this addition, and they follow a predictable arc. Everybody agrees it is important. Somebody proposes a paragraph in the project initiation documentation. A carbon figure appears in an appendix. And then, at the first stage boundary where the date is at risk, nothing about the sustainability aspect changes anybody’s behaviour at all.

That is not because people are cynical. It is because nobody has answered the question that makes a performance aspect real.

A tolerance you cannot breach is not a tolerance

Here is what makes the other six aspects work in PRINCE2. Each has a tolerance — a permitted deviation set at each level of management. Time might be plus two weeks. Cost might be plus five per cent. When a forecast exceeds tolerance, the project manager cannot simply proceed. They must raise an exception to the project board, which either grants more tolerance, changes the plan, or stops the work.

That mechanism is the entire engine of PRINCE2’s governance. Manage by exception only works because breaching a tolerance produces a mandatory event.

So the question for sustainability is not do we care about it. It is:

• What is the measure?
• What is the tolerance on that measure?
• Who has authority to grant more?
• And what happens, procedurally, when it is breached?

If you cannot answer all four, you do not have a seventh performance aspect. You have a paragraph.

Making it measurable without pretending

The obstacle people raise is that sustainability is not a single number. That is true, and it is not a reason to skip it — benefits are not a single number either, and we have managed to tolerance those for decades.

What works, in my experience, is choosing a small number of measures that are genuinely within the project’s control, and being honest that they are proxies rather than the whole truth.

For a technology project, the candidates that actually behave like variables are:

Estate change. How many physical or virtual servers, applications, databases and interfaces will exist at the end compared with the start? A migration project that adds a new platform and never decommissions the old one has failed on sustainability in the most literal, measurable way — you are now running two of everything. Tolerance this as a number of items and a date by which the old ones are off.

Energy or compute intensity. Where you can measure it — and cloud providers increasingly give you enough to — set a target for consumption per transaction or per user. It will be imperfect. Imperfect and tracked beats perfect and absent.

Hardware lifecycle. Devices replaced, devices refurbished, devices disposed of, and through which route. This is often the largest genuinely controllable sustainability variable in an IT programme and it is almost never in the project plan.

Longevity of what you build. How long is this solution expected to be viable before it needs replacing? A project that hits every date and delivers something with a four-year life where a seven-year life was achievable has made a sustainability trade-off that nobody recorded.

Travel and logistics, where the delivery model requires it.

Pick two. Put them in the business case with a baseline and a tolerance. Report them at every stage boundary alongside cost and time. That is all “adding a performance aspect” means.

The trade-off is the point

There is an uncomfortable truth in adding a seventh variable, and it is better said out loud.

Performance aspects exist to be traded. That is why they are aspects and not principles. If sustainability can never be traded against time or cost, it is not a performance aspect — it is a constraint, and it belongs in the project’s definition rather than in its tolerances.

Which means the useful conversation at a project board is precisely the one people find awkward: we can hit the September date, or we can decommission the legacy estate before we go live, but not both — which do you want, and will you record the decision?

I would far rather see a project board consciously choose the date and write down that decommissioning slips to the following quarter, with an owner and a date, than see a sustainability section that nobody has ever had to defend. The first is governance. The second is decoration.

Version 1 of PRINCE2 Agile had a name for this kind of conscious trade-off — fix and flex — and a hexagon to draw it on. Six aspects, six sides. The seventh aspect broke the geometry, and fix-and-flex and the hexagon have both dropped out of the Version 2 syllabi. The idea survives even where the diagram does not: something has to give, and a governance method is worth having only if it forces you to say what, in advance.

What happens when nobody sets the tolerance: HS2

The largest lesson available on estimating and governance in a megaproject is High Speed Two, and it is worth reading for what it says about baselines rather than about railways.

The programme was to build a new high-speed rail network. Phase 2’s northern leg and the Leeds leg were cancelled in October 2023, and Euston was redesigned.

What the official record shows about the numbers is remarkable. The Department for Transport and HS2 Ltd produced materially different estimates of the same scope: in 2024, DfT said £45–54 billion where HS2 Ltd said £54–66 billion, both in 2019 prices. They disagreed on methodology, assumptions, risk valuation and productivity savings.

The Public Accounts Committee’s view of that was blunt: the persistent disagreement “represents a failure of governance and oversight,” and “the Department has failed in its oversight and financial control over one of our most important public sector projects.”

Its summary judgement has become the most-quoted sentence in British project management: “The High Speed Two programme has become a casebook example of how not to run a major project.”

On contracts, the National Audit Office found that “HS2 Ltd has not driven the cost performance it expected through its contracts, and contractual incentives to control costs have not worked as intended.” Main civils construction costs rose £6 billion from 2020. After Phase 2 was cancelled, “HS2 Ltd had not adjusted to the significant changes in programme scope.”

An independent review by James Stewart, reporting in June 2025, found the governance structure “was not fit for purpose,” citing insufficient ministerial oversight and scrutiny, inadequate control by HS2 Ltd, and ineffective supplier incentives. All five recommendations were accepted.

By June 2026 the NAO’s estimate for the programme stood at £87.7 billion to £102.7 billion, an increase of £35.9 to £37.2 billion since 2020 excluding inflation — more than a doubling at the low end. Around £2 billion was spent on Phase 2 works that were then cancelled, including £592 million on land and property.

And then the sentence that should be read at every business case review anywhere:

“Had the current estimated costs been known when work began in 2020, this would have resulted in a benefit–cost ratio of between 0.3 and 0.4, which is categorised as ‘poor value for money’.”

That is the National Audit Office saying, in June 2026, that on today’s numbers the work should not have been started. Not that it went wrong — that the justification never existed at the price it actually cost.

PRINCE2’s first principle is ensure continued business justification, and it is a continuous obligation rather than a gate you pass once. HS2 is what it looks like when a business case is treated as an artefact produced at initiation rather than a number that must survive every stage boundary. The programme is, in the NAO’s phrasing, “now smaller than originally planned, while costing more and taking longer to complete.”

The transport secretary’s summary in June 2025 — “years of mismanagement, flawed reporting and ineffective oversight” — names reporting as one of the three, which is right and which most post-mortems miss.

Why Indian boards will get here first

If you are working in an Indian listed entity, the sustainability aspect is not a philosophical addition. It is a reporting obligation arriving from a different direction.

SEBI requires the top listed entities by market capitalisation to publish a Business Responsibility and Sustainability Report as part of the annual report, structured around the nine principles of the National Guidelines on Responsible Business Conduct, with assurance requirements phasing in for core indicators. Whatever your view of the framework, the practical consequence is that somebody in your organisation now has to produce auditable numbers on energy, emissions, waste and supply chain.

Those numbers get built from operational data. A significant part of that operational data is generated, or destroyed, by projects — the data centre you did or did not close, the devices you did or did not refurbish, the estate you did or did not decommission.

Which puts a specific question on the table for a project board: is our project’s sustainability reporting consistent with what the organisation will publish, and can it be assured? A project that reports a carbon saving the group’s assurance provider cannot substantiate has created a disclosure problem, not a benefit.

I sit on the other side of this table often enough to say what a director sees. A board gets a sustainability report full of aggregate figures, and no line of sight from those figures back to the decisions that produced them. The seventh performance aspect, done properly, is exactly that line of sight — a project-level record of what was traded, when, and with whose approval.

Six things to do at your next stage boundary

1. Name the measures. Two, not ten. In the business case, with a baseline.

2. Set a numeric tolerance on each, at project board and project manager level, the same way you do for cost.

3. Say who can grant more. If the answer is nobody, then it is a constraint, and it should be written as one.

4. Report it in the highlight report next to time and cost, every period, even when nothing has changed. An aspect reported only when interesting is an aspect nobody trusts.

5. Record the trade-offs explicitly. “We accepted a four-month delay to decommissioning in order to hold the September go-live date. Owner: X. Review: December.” That single sentence is worth more than a five-page sustainability annex.

6. Reconcile to what the organisation reports externally. Before you publish a project-level saving, check that the group’s reporting and assurance can stand behind it.

The honest conclusion

Adding sustainability to the performance aspects was the right decision, and PRINCE2 7 deserves credit for making it structural rather than an appendix.

But a performance aspect is defined by what happens when it is breached, and at the moment, in most organisations, nothing happens. The measures are absent, the tolerances are unset, the escalation route is undefined, and so the aspect exists in the documentation and nowhere else.

That is fixable this quarter, by one person, in about two hours, with a spreadsheet and a difficult conversation.

The alternative is that in five years somebody writes the report about your programme, and the sentence in it is the HS2 sentence — that had the real numbers been known at the start, the work would not have been justified.

Sources

• Purple Griffon, What’s new in PRINCE2 7 (seven performance aspects) — purplegriffon.com
• Knowledge Train, PRINCE2 7th edition (sustainability added as the seventh performance target) — knowledgetrain.co.uk
• PeopleCert, PRINCE2 receives major update (4 September 2023) — peoplecert.org
• Henny Portman, PRINCE2 7th edition (8 August 2023) — hennyportman.wordpress.com
• National Audit Office, HS2: update on the programme (2024) and subsequent report (June 2026), including the benefit–cost ratio finding
• House of Commons Committee of Public Accounts, reports on High Speed Two
• James Stewart, independent review of HS2 governance (June 2025)
• Department for Transport, statement on HS2, 18 June 2025
• Securities and Exchange Board of India, Business Responsibility and Sustainability Reporting requirements under the SEBI (Listing Obligations and Disclosure Requirements) Regulations, 2015