UK Prime Minister Liz Truss’ Armed Forces Minister threatens to quit her Cabinet live on air

Just when it looked like matters couldn’t get any worse for Liz Truss, one of her inner circle made his feelings clear on live radio.

UK Prime Minister Liz Truss has been dealt another cruel blow as one of her ministers threatened to quit her Cabinet live on air.

Armed Forces Minister James Heappey vowed to resign if Ms Truss fails to meet her commitment to raise defence spending to three per cent of GDP by 2030.

And in what could be an even bigger blow to Ms Truss’ ever-slimming hopes of survival as Prime Minister, Mr Heappey’s boss, Defence Secretary Ben Wallace, would also quit if the spending promise was not met, a source told The Guardian.

Mr Wallace “will hold the prime minister to the pledges made”, the source said. “Current world events, and allies commitments show that defence is not a ‘discretionary’ spend but a priority,” they added.

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UK Prime Minister Liz Truss (Photo by Sean Smith - Pool/Getty Images)

Former soldier Mr Wallace is popular among the party and members of the public thanks to his no-nonsense approach, and he has avoided embroiling himself in speculation about replacing Ms Truss - just as he did when his name was floated following the resignation of Boris Johnson.

But new Chancellor Jeremy Hunt has said no department is safe from cuts to help steady the markets, raising the prospect of Ms Truss reneging on the promise she made about defence spending as the war in Ukraine rages on.

Mr Heappey was asked if he would resign if the three per cent spending commitment was dropped during an interview on LBC radio.

“Yeah, but no one said ... that 3% is not going to happen by 2030,” he replied.

Armed Forces Minister Minister James Heappey arrives at Downing Street on Tuesday (Photo by ADRIAN DENNIS / AFP)

He later told Sky News: “The commitment the Prime Minister made is three per cent by 2030 and to be clear like the secretary of state [Mr Wallace] that’s something that I believe must be delivered given the need to keep our nation safe given increasingly uncertain times.

“If in the very immediate term there is a requirement to look at what we can do to help the Treasury out that’s a discussion for the Chancellor to have with the secretary of state.”

Mr Heappey was also asked if Ms Truss could afford to make any more mistakes, after apologising for her ‘mini-Budget’, which sent mortgage rates soaring, led to the Pound dramatically decreasing in value and saw her party plunge to new lows in the polls.

“I suspect given how skittish our politics are at the moment, not very many,” he said.

“I don’t think there’s the opportunity to make any more mistakes.”

Defence Secretary Ben Wallace arrives for the weekly cabinet meeting at 10 Downing Street. (Photo by Dan Kitwood/Getty Images)

Mr Hunt has refused to ringfence any departments, meaning defence, health and pensions may also face spending cuts.

Currently the UK spends 2.1 per cent of its GDP on defence, which is planned to increase incrementally until it hits three per cent by 2030. In real terms, that’s around £100 billion ($179 billion AUD) a year.

Ms Truss is under increasing pressure to quit as PM - just a matter of weeks after taking office.

Five of her MPs have publicly called on her to go and dozens more privately want her out, however there is disagreement among MPs about who should replace her and by what mechanism.

Ms Truss has vowed to stay on as leader and she cannot face a leadership challenge for an another 11 months.

The former Chancellor Rishi Sunak and Leader of the House of Commons Penny Mordaunt cane second and third in the recent leadership contest that saw Ms Truss become PM.

Mr Sunak is keeping his cards close to his chest but allies say he still wants the top job.

Ms Mordaunt has called for the party to unify around Ms Truss.

Mr Wallace has also been touted as a possible leader but he has expressed no interest in usurping Ms Truss.