Plans for further cuts to the police force that guards Britain's nuclear arsenal could be "catastrophic", a leading officer will warn.
The Ministry of Defence Police (MDP), which has responsibility for guarding key MoD assets including Trident, is to make the cuts to achieve a £12.5 million saving, a move which will "harm national security", Eamon Keating will say.
Mr Keating, the national chairman of the Defence Police Federation (DPF) - the staff association representing MoD police officers, will say the decision prioritises financial savings over the protection of critical assets such as the nuclear deterrent.
The civilian force, whose officers are all firearms trained, is currently understaffed with around 2,300 officers when it should have around 2,600, according to the DPF.
The force plans to "re-set" its complement strength to below 2,300 officers and abandon recruitment, which Mr Keating will warn means there are fewer armed officers available for deployment in the event of a national incident as part of Operation Temperer - enacted just last month in the wake of the Manchester bombing.
In a keynote speech to the federation's annual conference on Thursday, Mr Keating will say: "After a decade of budget and personnel cuts, it beggars belief the MoD would demand a further £12.5 million from the police force entrusted with guarding Trident.
"And it's simply unacceptable for the MoD Police leadership to find this saving by shifting the goalposts and imposing a real-terms cut in our number of officers.
"We need to be very clear that, at a time of significant threat, this represents a reduction in the country's armed policing capacity and is damaging to public safety and national security.
"This 'reset' is an ill-considered decision that prioritises cost over security, and makes no sense given the financial value of the assets we protect."
The MDP boasted around 2,600 officers a year ago, but the workforce had already been reduced by a third due to budget cuts in 2010.
The federation will also call on the Government to provide further details on plans in the recent Conservative election manifesto for an "Infrastructure Policing Force" to be created through a merger of the MDP, the Civil Nuclear Constabulary and British Transport Police.
The DPF will express concern at the imposition of Home Office fitness standards on the MoD police and demand Government action to change the retirement age of officers currently expected to work into their mid-60s.
Mr Keating will add: "The Government must urgently rethink this catastrophic decision that further undermines police officers hamstrung by fitness tests inappropriate to the job they do, and a pension age different to the Home Office and Armed Forces."
The two-day conference is taking place at Stansted Airport in Essex.
A Ministry of Defence spokesman said: "We are confident that the strength of our force keeps our people, sites and equipment safe.
"It also enables us to play our part in protecting the public, as we did when we supported the armed police response to the tragic events in Manchester last month."