Projects where contractors were appointed at RIBA Stage 4 recorded average cost overruns of 17.35%, compared to near-flat performance on projects where contractors were engaged at RIBA Stages 0-2, according to the largest quantitative analysis of early contractor involvement ever undertaken in UK public sector construction
Published by the Centre for Construction Best Practice (CCBP), Constructing Certainty analysed 412 public sector projects delivered by 55 contractors across the UK, mapping contractor appointment timing against final cost and programme performance.
The findings provide one of the clearest empirical datasets yet linking late contractor appointment to increased project risk, cost escalation and programme overruns across public sector construction.
Robbie Blackhurst, chair of CCBP, stated: “For too long, lowest-price procurement, compressed timelines and late market engagement have pushed risk down the supply chain with severe consequences for our industry and for the taxpayer.
“Project failures have frequently been attributed to a lack of early contractor involvement, but until now the industry has lacked the large-scale data to prove it.”
Contractor appointment is ideal at RIBA Stages 0-2
Projects where contractors were engaged at RIBA Stages 0-2 recorded average cost variances of between -1.79% and -1.62%, broadly delivering on or below budget.
In contrast, projects appointed at RIBA Stage 3 recorded average cost overruns of +8.56%, rising to +17.35% at Stage 4.
Programme performance followed a similar pattern. Stage 3 projects averaged programme overruns of +11.53%, while Stage 4 projects averaged +12.84%.
Projects adopting procurement approaches with weaker outcomes
The report also found that 63% of projects in the dataset were still procured at RIBA Stages 3 or 4, suggesting that most public sector construction projects continue to adopt procurement approaches associated with significantly weaker delivery outcomes.
CCBP estimates that, when applied illustratively across the government’s £725bn ten-year infrastructure pipeline, late-stage contractor appointment could expose projects to more than £125bn in avoidable cost risk. Earlier engagement models corresponded with indicative savings of up to £13bn across the same pipeline.
The report draws on project-level data spanning healthcare, education, civic and infrastructure schemes, with contractor appointments mapped across RIBA Stages 0–4. Healthcare and education projects accounted for 66% of the sample.
Contributing organisations span the full breadth of the construction supply chain, from major contractors including Morgan Sindall, Wates, Kier, BAM, Galliford Try, and GRAHAM, consultancy firms such as Turner & Townsend, Pick Everard and Avison Young, to SMEs and specialist subcontractors operating across demolition, fit-out, facades, roofing, M&E and groundworks.
Early contractor involvement is crucial for project delivery
Academic partners supporting the report said the findings provide one of the clearest quantitative cases yet for reforming public sector procurement behaviour regarding contractor engagement.
Dr Kell Jones of the Bartlett School of Sustainable Construction at UCL said: “The sector has long been locked into established procurement behaviours despite widespread recognition that greater integration improves outcomes.
“What makes this report significant is the scale of quantitative evidence linking early contractor involvement with improved cost and programme performance across public sector projects.”
How procurement timing affects supply chains and decision-making
The research also highlights the impact procurement timing has on supply chain involvement and decision-making.
Contractor input into buildability and programme ranged from 96% to 100% on projects appointed at RIBA Stages 0-2 but fell to 49% by Stage 4. Early supply chain cost advice similarly declined from 100% at Stages 0–1 to 69% at Stage 4.
The report argues that late-appointment models continue to shift disproportionate risk downstream at a time when the sector is already under significant financial pressure. Construction recorded 3,931 insolvencies in 2025 – representing the highest proportion of any UK sector and a 22% increase on pre-pandemic levels.
Only 6% of survey respondents strongly agreed that current procurement routes adequately support meaningful ECI.
Recommendations of the report
On the basis of the findings, CCBP is calling on government and public sector clients to:
- Mandate early involvement by RIBA Stage 2 on public sector capital projects above £5m, proportionate to project complexity and risk
- Strengthen public sector capability and confidence in ECI by providing standard guidance, templates and training to make early engagement consistent and auditable
- Introduce mandatory value checks, so contracts are not awarded on lowest price alone
The report places particular emphasis on refurbishment and renewal schemes, where hidden conditions and operational constraints often increase delivery risk if contractor expertise is introduced too late.
Simon Arnott, managing director construction north at Morgan Sindall, explained: “The evidence in this report reflects what we see in practice: the earlier delivery expertise is brought into a project, the greater the opportunity to influence outcomes.
“This isn’t about any single procurement route; it’s about making better decisions when it still matters. Early engagement allows contractors and our supply chains to drive innovation, challenge assumptions, and add real value through buildability, sequencing, and intelligent solutions.”
He concluded: “It moves our role beyond delivery alone, bringing us onboard as a collaborative, long-term partner in shaping successful projects. With significant public investment ahead, that shift is critical to improving certainty, performance and overall outcomes”.
CCBP says the recommendations are intended to move ECI from advisory guidance to a measurable, auditable delivery standard across public sector procurement.
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