Five infantry battalions are expected to be axed and other units merged or turned into reservists in the biggest overhaul of the Army in more than a century, under plans to be announced today.
Defence Secretary Philip Hammond will set out how the regular Army will be cut from 102,000 troops to 82,000 by the end of the decade - its lowest level since the Napoleonic Wars.
The plan - known as Army 2020 - is expected to see it split into two, with a reaction force, ready to respond to emergencies around the globe, and an adaptable force capable of carrying out a range of tasks and commitments.
Mr Hammond has said the changes - drawn up by Lieutenant General Nick Carter - will provide the basis of a smaller, more flexible and agile Army into the future.
But the prospect of losing historic units has been the cause of intense anguish within the service.
The Daily Telegraph disclosed this week that one officer, Brigadier David Paterson of the Royal Regiment of Fusiliers, had written to the head of the Army expressing his bitter disappointment at plans to axe one of its two battalions.
In his letter to General Sir Peter Wall, Chief of the General Staff, Brig Paterson said the proposal ‘cannot be presented as the best or most sensible military option’.
Other units under threat are reported to include the Yorkshire Regiment, the Royal Regiment of Scotland, the Royal Welsh and the Mercian Regiment.
Mr Hammond, who will set out details of the proposals in a statement to the House of Commons, has acknowledged that they have involved some ‘difficult’ decisions.
But he said that cuts could not be avoided, with the demands for strict financial discipline under the Government’s 2010 Strategic Defence and Security Review.
Under the plans, reductions in regular Army strength would be offset by increases in part-time reservists, with the Territorial Army doubling in numbers from 15,000 to 30,000.
As well as providing specialist capabilities - such as medics and intelligence - reservists would be used to reinforce infantry battalions on deployment.
The Army would also be required to make greater use of civilian contractors in areas such as logistics support in order to concentrate military capability on the frontline.
Colonel Bob Stewart, a Conservative MP and former commanding officer with the Cheshire Regiment who sits on the defence select committee, said cutting troops was not the right way forward but the Government had been left with no option.
Asked if the Defence Secretary was putting the nation at risk, he told BBC Breakfast: ‘Every defence secretary has to balance exactly what the risk is. We just don’t know what the risk is.
‘If you reduce the numbers available you have less options, you have less flexibility, you have less power, that’s a fact.
‘So if you reduce the numbers you are actually putting the nation more at risk, yes, but equally we don’t have much of a choice.’
Labour MP and former paratrooper Dan Jarvis said he was ‘very sad and very concerned’ about the downsizing of the army.
He said: ‘We should absolutely be looking at ways to save money but we should be looking incredibly carefully at the way in which we provide our national security, and a key component of that are our armed forces.
‘They are about to be reduced by a significant amount, the army is going to go from 102,000 to 82,000 in a very uncertain world.
‘I am not convinced at all that is the right thing to do, I am not convinced that at the end of that process we will have an armed forces that will be able to do the kind of things we might want them to do in the future.’
General Lord Dannatt, former head of the Army, said his successor Sir Peter Wall and senior officers were ‘making the best of a reduced deck of cards that they have been dealt’.
He told BBC Radio 4’s Today programme there were ‘some risks’ attached to sharp reductions in the size of the Army.
‘It won’t be capable of conducting two operations simultaneously of the scale of Iraq and Afghanistan as we have done over the last 10 years,’ the peer said.
‘It will mean that we can do less but we will still do an enormous amount.’
Lord Dannatt said there was a danger the British military could be ‘exposed’ in the short term, and ministers should be ready to change the shape and size of the forces quickly.
‘Let’s hope that the next decade is a rather more peaceful decade than the last decade but I wouldn’t bet on it,’ he added.