The BCIS All-in TPI was never built to measure MEP.
So what is the inflation allowance in your MEP cost plan actually measuring?
A common approach to inflation in an MEP cost plan is to use a general tender price index to inform the allowance. The BCIS All-in TPI is a broad measure of tender price movement. Its published basis records that the project indices underlying the series excluded M&E and other specialist trades. It is tracking the market for the building, not the market for its services.
1. Why the headline needs context
BCIS reports that the All-in Tender Price Index rose by 3.2% in the year to 3Q2026, while its General Building Cost Index is forecast to rise by 4.5%. Input costs and tender prices describe different things: contractors price against workload, order books and competition as well as underlying cost, and 77% of the latest TPI Panel reported contractors eager to tender. Competition is absorbing cost pressure for now, and panel members describe the present as an opportune time to build for clients with viable projects. For building services there is a second point. BCIS publishes the basis of the All-in TPI with every release. It records that the project indices underlying the series excluded M&E and other specialist trades, for example facades, and that the latest-quarter estimate is a panel consensus on movement across accepted tenders. The series is a broad measure of building tender prices, not an MEP-specific one.
The question for any MEP cost plan is not whether the inflation allowance is the right percentage. It is whether the allowance is measuring the right thing.
2. The market beneath the headline
The BCIS commentary also points at building services specifically. Large, complex projects and those exposed to MEP specialists are identified as carrying greater price risk. The panel reports package cost pressure in M&E, sprinklers, security and specialist labour, and anecdotal evidence that copper prices are running 10 to 20% above expectation in some cases. Capacity is part of the picture. Data centre construction and the New Hospital Programme are cited as competing for the same specialist M&E resource, and insolvency among M&E subcontractors is highlighted as a delivery and cost-stability risk.
Do not replace a broad market index with a broad MEP premium. Replace broad assumptions with better evidence as the project develops, and show which is which.
3. A £10 million MEP cost plan is not one market
An MEP cost plan aggregates electrical distribution, HVAC plant, controls, life-safety, security, lifts and a substantial installation labour component. These packages have different drivers, and there is no reason to expect them to move together or with the headline index.
4. What a useful MEP cost plan should show
In this market an MEP cost plan should separate four things rather than blend them into a single inflation line: market movement, package movement, market exposure and cost firmness. The fourth is often the least visible to the reader, and it is the one THM has formalised. Every rate and allowance on our cost plans is graded across scope, quantity and pricing as firm, supported or provisional.
5. Where this leaves the cost plan
For us the answer is not another index. We would actually be wary of producing a single MEP index because it risks repeating exactly the same problem one level down. A switchgear package, a sprinkler package and an ICT package are not moving for the same reasons. The better answer is to understand what is driving each part of the cost plan, use the best evidence available and be clear about how firm that evidence is.
1. BCIS, "BCIS tender price index: estimate of tender price inflation, 3Q2026", 23 September 2026.
2. BCIS, Dr David Crosthwaite, "Construction input costs are outpacing tender prices. How long will the gap hold?", 24 September 2026.
3. BCIS, "BCIS Tender Price Index Panel", methodology note.
4. Teddy Henry Metrics, THM Insight Series, cost plan firmness grading methodology, forthcoming.