The Nimrods are expected to be out of service until early summer
All Nimrod aircraft that have not had a vital safety modification are to be grounded by the Ministry of Defence, the BBC has learned.
The Nimrods, all based overseas, will be withdrawn on 31 March in order to replace engine bay hot air ducts.
The MoD has said there will be no impact on operations.
The move follows the deaths of 14 servicemen in a Nimrod crash in 2006. The coroner at their inquest called for the entire fleet to be grounded.
The accident, involving an aircraft based at RAF Kinloss in Moray, happened in September 2006 shortly after air-to-air refuelling when leaking fuel came into contact with a hot air pipe.
At the inquest last May, coroner Andrew Walker said the aircraft had "never been airworthy," but Defence Secretary Des Browne insisted they were safe to fly.
Inside a Nimrod as safety measures are explained - first broadcast August 2008
Graham Knight, father of Sgt Ben Knight, 25, who died in the crash, said it was "quite bizarre" that ministers appeared now to have changed their minds.
"It shows what we all said after the inquest that these aircraft weren't safe to fly until after this work had been done," he told the BBC.
"Have they been flying them since [the inquest] without these safety modifications being done?
"Well, obviously the answer is yes. Safety has been compromised since the inquest."
The modification work on the hot air ducts - and also to replace aircraft fuel seals - was due to be completed by 31 March, but has been delayed.
In a written statement to the House of Commons, Defence Minister Bob Ainsworth said that the temporary halt to overseas operations "will allow us to free up the maximum number of aircraft for the modification programme while also allowing Nimrod to continue with its critical homeland security tasks".
It is a further example of the complete inability of this government to get a grip on their defence procurement programme
Dr Liam Fox Shadow defence secretary
The reallocation of engineering staff from the Nimrods' home base at RAF Kinloss to the modification programme at RAF Waddington in Lincolnshire "will cause a temporary reduction in routine UK-based Nimrod flying but will not affect our ability to protect UK interests at home," he added.
The MoD said there would be no operational impact in Afghanistan because they plan to use other UK and coalition aircraft to cover any shortfall.
But the BBC understands the withdrawal - due to last until early summer - could have an impact on training in Britain.
'Lives at risk'
Angus Robertson, from the SNP, represents the constituency around RAF Kinloss. He told the BBC the crash had been a "hammer blow" to the community.
"I think there are questions around why these improvements couldn't be made in time, but far more important than that is the safety of the crews that fly these aircraft, which after all are nearly 40 years old," he said.
It is disgraceful that it has taken so long for ministers to take action to ground unsafe aircraft
Nick Harvey Lib Dem defence spokesman
Shadow defence secretary Dr Liam Fox said that by releasing the news in a written statement the government was "avoiding answering awkward questions" about the issue.
"It beggars belief that even after 18 months, the MoD and its contractors have failed to modify these aircraft which are undertaking critical surveillance operations in Afghanistan," he said.
"It is a further example of the complete inability of this government to get a grip on their defence procurement programme."
Liberal Democrat defence spokesman Nick Harvey said: "This is in effect an admission by the government that the Nimrod fleet is not safe to fly, and has not been for years.
"It is disgraceful that it has taken so long for ministers to take action to ground unsafe aircraft which have already claimed the lives of our service personnel and are still putting others at risk.
"It also must be asked why it is deemed safe for these aircraft to continue to fly for a moment longer, let alone another three weeks, without the necessary replacement of their hot air ducts."
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