Working on a site in the remote Yorkshire countryside, the task of building the UK’s first all-electric prison was always going to have its challenges for tier one contractor Kier.
HMP Millsike’s rural location in Full Sutton, near York, led to difficulties attracting labour, as well as infrastructure issues when transporting plant to the site.
And that was before the team faced the unenviable task of clearing the ground of hundreds of pieces of live ammunition left from the site’s former days as an RAF base.
But the UK’s third-largest contractor has overcome the obstacles, adding another project to its growing prison portfolio.
HMP Millsike is the UK’s first prison to be delivered as part of the Alliance 4 New Prisons (A4NP), which will see the Ministry of Justice delivering 20,000 new prison places overall. The A4NP, which also includes Laing O’Rourke and Wates, will deliver 6,000 of those.
Ahead of the prison opening its doors on 27 March, Construction News got to observe first-hand the fruits of the 128-week project, which was completed to schedule for client the Ministry of Justice (MoJ).
Kier’s project lead Paul Wright said the job was completed on time and to budget despite its scale and complexity.
“We carried out six months of enabling work getting the land prepared so we could start piling on day one,” he said.
“It was a former RAF base and when we surveyed all the land there were 4,500 objects on it – 230 live. We had to dig a pit on site to explode them.
“We had 88 subcontractors and at its peak we had around 1,000 people on site each day.”
The £400m Category C prison, built to house 1,500 inmates in six blocks, is the size of 39 football pitches and is the first in the UK to run entirely on electricity, with more than 8,500kWh of renewable energy being generated to power it.
Solar panels, heat-pump technology and more efficient lighting systems mean it will use approximately a quarter of the energy used to heat traditional Victorian prisons.
The power to the prison was provided by Northern Power, which ran a 20km electricity line into a main switch which then feeds the prison and five sub-stations with generator back-up on site.
“It is the first green prison in the country and other new-builds will follow in the same way,” Raj Singh, the MoJ’s principal project manager, told CN.
“Kier was very proactive right from the beginning to improve the [efficiency of the] supply chain and it has been very successful,” she said.
“A lot of the plant was built offsite and lowered in. It increased productivity and was more than 25 per cent faster than traditional methods.”
The firm saved time by using 3,482 continuous flight auger piles – 600mm in diameter and 10 metres in depth – to support the 12 buildings.
The mechanical and electrical (M&E) plant was built offsite and lowered into the building, reducing labour costs and time.
“Our approach to the scale of the M&E used is completely transferable to other projects,” Wright added.
“The M&E embraced design for manufacture and assembly by utilising offsite-manufactured riser units and horizonal racks. There were 1,200 factory-assembled units and, in addition, there were 74 plants skids made offsite.”
A major challenge they faced was the site having a high water table, with ground water just 1.5 metres below the surface of the site.
As the permanent design called for deep drainage and structures, including cable ducts, Kier employed the services of a hydrologist to assess the ground and check the water infiltration rates.
“It subsequently allowed us to design a dewatering system,” Wright said.
“The system proved very successful and diverted water down to 3.5 metres below ground by way of a well point dewatering and silt buster pumps.
“The water was directed by a series of 150mm pipes to three silt buster pumping stations and beyond into the local ditch network.
“The discharge was licensed by the Environment Agency and we had a restricted outflow limit. A further three settlement ponds were constructed to allow for any additional surface water pumping.”
As part of the project, Kier installed 48km of underground ducts and 20km of underground drainage, and created seven permanent attenuation tanks which can hold five million litres of water from the prison roofs and hard landscape areas.
Drone defence
In a UK first, the firm installed specialist windows without bars that can stop drones carrying illicit items accessing the prison.
They are made of ballistic reinforced glass that is so robust “it would take 90 minutes for an inmate to try and break if armed with items within the prison”, an MoJ source said.
The build also comprises 11,628 precast concrete components, 28,500 paving slabs installed on the roof and 4.1km of prison fences. The centre includes educational facilities to teach trades including bricklaying and carpentry.
Lord chancellor and secretary of state for justice Shabana Mahmood MP hailed the prison as a blueprint for the future and described Millsike as “a huge step in our plan to add 14,000 extra prison places by 2031”.
The facility’s opening is a major milestone in the government’s 10-year prison capacity strategy published in December. This plan includes 6,400 places through new houseblocks and 6,500 places via new prisons.
In February, Kier was appointed to build a £1bn prison in Glasgow. The facility will replace the nearby HMP Barlinnie, which was built in 1880 and is Scotland’s largest prison.
It expects to complete the project in 2028 and has been carrying out early works on the site since October.