Keir Starmer was last night under growing pressure to quickly hike defence spending by his own MPs and defence chiefs.
They warned that without hiking it to at least 2.5 per cent of gross domestic product (GDP) within days, the Prime Minister risked failing to meet his promise that the UK will play a ‘leading’ role in keeping the peace in Ukraine.
Sir Keir yesterday flew to an emergency summit in Paris after pledging he was ‘ready and willing’ to deploy soldiers alongside European and US personnel as part of a ceasefire deal.
But experts believe a collective force of around 100,000 will be needed due to the vast size of the border between Russia and Ukraine.
The Army is currently at its smallest size since Napoleonic times.
Former head of the Army Lord Dannatt said the UK would struggle to deploy more than 10,000 troops to the frontline in Ukraine at any one time.
He told the Mail: ‘The fact is, Keir Starmer might be ready and willing but the British Armed Forces aren’t ready – although of course we would always be willing.
‘I think we’re a relatively long way from a situation whereby [Vladimir] Putin would accept a peacekeeping force to stand between Russian forces and Ukrainian forces in Ukraine.
‘I can’t see it happening anytime soon.
‘But if we did find ourselves in that situation, it could be that we collectively require around 100,000 troops. It’s a 700km front line, which is huge.
‘Assuming many countries would be willing to contribute contingents to that, I could see Britain having to contribute somewhere between 5,000 to 10,000 troops.
‘But remember we work in 24-month cycles, so with six-months deployment for each, we need four groups for the rotation. So we actually need 40,000 troops in total if we want 10,000 on the frontline at all times.’
He said the UK would ‘struggle’ to achieve this but that it was possible.
Warning that Sir Keir must boost defence spending now to also invest in much-needed new equipment, he added: ‘He’s got to start increasing the funding for defence now and we’ve got to start acquiring more of the equipment that we would need.
‘We’ve cut tactical airlift aeroplanes, we’ve cut the number of helicopters, we’ve not refurbished the Warrior infantry fighting vehicles, we gave all our artillery to Ukraine early in the war.
‘We’re not in a good position, unless there’s going to be a massive injection of funds now to make ourselves capable.
‘This crisis, frankly, could define Keir’s premiership.’
He said it would likely take three to six months before troops were ready to deploy.
The UK currently spends 2.3 per cent of GDP on defence.
Although Sir Keir is pledging to boost this to 2.5 per cent, he is refusing to set out a timetable for it until at least the spring.
But Lord Dannatt said he should set it out within days so defence chiefs can plan properly and Sir Keir doesn’t go ’empty handed’ to Washington next week for talks with US President Donald Trump, who has demanded that Nato allies increase defence spending to around 5 per cent of GDP.
He also said the Armed Forces needed more like 3 per cent to 3.5 per cent of GDP to be spent on defence, and that in the long-term the UK should even think about hiking it to 5 per cent.
Two Labour MPs also piled pressure on Sir Keir last night, suggesting the UK needed to raise spending to nearly 5 per cent of GDP. Melanie Ward, the MP for Cowdenbeath and Kirkcaldy, and Aylesbury MP Laura Kyrke-Smith said the Prime Minister needed to ‘move fast and be far more ambitious’ than the 2.5 per cent target.
In a joint article for Politics Home, they wrote: ‘We risk being stuck in squabbles about basis percentage points of defence spending when the reality is: the stakes are far too high for that.
‘Planning to reach 2.5 per cent of GDP spending on defence at a distant future moment is no longer sufficient.’
It came as it emerged that some Government departments have been asked to model spending cuts of up to 11 per cent to find the cash to boost defence.
Departments had been told to expect cuts of up to 5 per cent.
Labour MPs also criticised Sir Keir by insisting Parliament should get a vote on whether troops are deployed to Ukraine.
Veterans such as Graham Stringer and Diane Abbott were among those saying any deployment should first be green-lighted by Parliament.
The Prime Minister’s spokesman did not rule out a vote but said ‘we’re getting ahead of ourselves’ because no ceasefire deal has yet been reached.