HMP Millsike, Full Sutton, Yorkshire, UK

NEC has been used to deliver Britain’s greenest prison on time and budget. HMP Millsike at Full Sutton near York is the country’s first prison to be fully electric, with a mix of grid power, 8,500 kWh of solar energy, a hybrid battery solution and heat pumps helping win a Breeam ‘excellent’ sustainability rating. The project has been shortlisted for Social Infrastructure Project of the Year in the 2025 British Construction Industry Awards.

Completed in March 2025 by Kier, HMP Millsike is the first of four new prisons being delivered by an NEC4-based alliance called Alliance 4 New Prisons (A4NP). Appointed by the Ministry of Justice, the A4NP alliance of Kier, Laing O’Rourke and Wates holds a FAC-1 Framework Alliance Contract worth over £1 billion with NEC4 terms awarded in July 2022 through Crown Commercial Service’s construction works and associated services agreement. NEC Users’ Group gold member Mace was appointed alliance manager. This alliance model allows the members to focus on repeatability and continuous improvement to drive better performance in capital delivery and lifecycle costs. 

A4NP members are building prisons under NEC4 Engineering and Construction Contract (ECC) Option A (priced contract with activity schedule) terms, starting with Kier at Full Sutton. They are also collaborating on a common delivery methodology that prioritises modern methods of construction, with standardised components, platform design for manufacture and assembly, and digitisation of construction.

HMP Millsike provides nearly 1,500 new category C prison places for men in six four-storey reinforced concrete house blocks. There are also several steel-frame ancillary buildings on the 25 ha site for workshops, training facilities, offices and a kitchen. Modern methods of construction were used extensively for the buildings, including 12,998 precast concrete components and 198 four-storey-high mechanical and electrical risers in the house blocks. 

The design was produced by NEC Users’ Group gold member Pick Everard, part of Perfect Circle. The Ministry of Justice engaged the firm in late 2020 under a NEC3 Professional Services Contract (PSC).

Collaborative delivery

Melissa Dudley, construction commercial director at the Ministry of Justice, says NEC4 was chosen for A4NP because it supported collaborative delivery and early supplier involvement across multiple prison builds. ‘NEC4’s integration with the FAC-1 alliancing form of contract enabled shared objectives and flexible governance while aligning with government policy and the Construction Playbook. This structure allowed for joint risk mitigation, early design input and efficient use of shared supply chains.’

 She says the ECC Option A that governed HMP Millsike’s construction supported early and frequent communication between the client and contractor teams. ‘It provided the structure and rigour to ensure risks and issues were dealt with quickly and collaboratively. Clear responsibilities, risk allocation and mechanisms to resolve problems meant few escalations at a senior level, allowing both teams to focus on delivering on time and on budget.’

Andy Burley, project commercial director at Kier, says NEC4 fostered clear communication and collaboration. ‘It facilitated early engagement with our specialist supply chain, helping us to maximise design for manufacture and assembly and creating an environment where everyone was working towards common goals from day one.

‘That collaborative environment meant we were able to integrate mechanical and electrical design with precast concrete, moving more activity to controlled factory environments, reducing waste and significantly increasing productivity.’
             
Stuart Rutter, associate director at Mace, says NEC4’s early warning system proved invaluable in highlighting risks at the earliest stage. ‘This allowed the project team to manage issues collaboratively and before they had a significant impact.’

He says that the structured approach to NEC4 compensation events also meant that changes were priced, discussed and agreed much closer to the point of occurrence, giving far greater control over time and cost. ‘Combined with the transparent open-book reporting, NEC4 created a culture of trust and accountability, with all parties able to make informed decisions and maintain budget certainty.’

Benefits of using NEC

• NEC4 supported collaborative delivery and integrated well with the FAC-1 alliance contract, enabling shared objectives and flexible governance.

• ECC Option A supported early and frequent communication between the client and contractor teams.

• NEC4 early warning system allowed the project team to manage issues collaboratively before they had a significant impact.

• NEC4 compensation events meant changes were priced, discussed and agreed close to the point of occurrence, giving more control over time and cost.