The Defence Fire and Risk Management Organisation provides fire cover to 300,000 Ministry of Defence employees and strategic assets dispersed across 4,600 sites with 45,000 buildings worth more than £100bn. It has 2,000 military, civil service, locally employed civilian and contractor staff.

The award of the contract was delayed following a legal challenge from Serco Ltd, the other final bidder. The MOD and Serco Ltd agreed an out-of-court settlement of £10m.

The government says the project will improve safety for firefighter personnel and those they protect, because the contract will see investment in new equipment, technology and training “faster than it otherwise would”.

The government “expects” the contract to deliver significant financial savings over its lifespan.

But Prospect told MPs in 2018 that the true cost of providing fire risk management to defence is more likely to be around £1.2bn (when the governance organisation, defence fire safety regulator, Cyprus locally employed civilians, United States Visiting Forces staff, RAF and Royal Navy firefighters and extant multi-activity contracts are included).

The union also questioned whether statements made about projected savings on pensions costs were accurate.

Garry Graham, the union’s deputy general secretary said: “Prospect does not believe that the projected savings can be delivered without increasing the risk to defence.

“It’s outrageous that the existing in-house provision has been systematically run down with massive cuts and underfunding stifling its ability to deliver efficiencies and introduce new technology.”

Initially, around 560 MOD civil servants, mainly firefighting personnel, are expected to transfer to Capita under the Transfer of Undertakings (Protection of Employment) regulations.

The Defence Fire Training and Development Centre at Manston in Kent will close and training will be transferred to Capita’s fire training facility at Moreton-in-Marsh.

Existing fire and rescue services provided to the Atomic Weapons Establishment in Aldermaston, the Defence Science and Technology Laboratory in Porton Down and at US visiting forces bases in the UK are unaffected by the changes.

The Royal Air Force and Royal Navy will continue to employ firefighters. But the number of firefighters in the RAF will be reduced over time “due to the introduction of new technology” and some roles becoming sponsored reserves.