Rishi Sunak is set to unveil a £5billion boost to UK defence spending on a trip to the US this weekend.

The PM will announce the multi-billion uplift as he holds talks with Joe Biden and Australian counterpart Anthony Albanese over the AUKUS nuclear submarine pact.

However, the settlement is not expected to be anywhere near the £8billion-£11billion extra Defence Secretary Ben Wallace has been demanding to deal with surging inflation.

The department is seen as particularly exposed to inflation due to its huge equipment projects. 

Mr Wallace suggested he has not given up on his lobbying today, saying he is 'pretty confident' the military will get the investment it needs. 

Asked at Conservative Home's defence and security conference on Monday whether he was confident he would receive the investment the armed forces required, said: 'I'm pretty confident, yes.'

As well as dealing with inflation, which stands at about 10% according to some metrics, the senior Conservative minister said Russia's attack on Ukraine had changed the timetable for when military investment would be required.

He said £24billion of armed forces funding, announced by Prime Minister Rishi Sunak in 2020 when he was chancellor, was designed to plug 'historical black holes' but also kick-start the process of updating British Army equipment that was 'desperately in need of replacement'.

Stating that some Army upgrades were 15 years overdue, Mr Wallace continued: 'We were prepared to take some risks in the timeframes of bringing in new capability.

'Then, of course, (Russian president Vladimir) Putin invades Ukraine and that changes some of those middle-of-the-decade timetables that we were prepared to take a risk in.

'The negotiations I'm involved in are about how I can bring some equipment forward in order to mitigate those risks.'

He repeated his assertion that the British Army had been 'hollowed out' over a 30-year period by successive governments of every colour.

Mr Wallace also called for the UK to move to a 10-year budget framework for defence to provide long-term stability and avoid waste when it comes to military procurement.

Tory MPs have been backing Mr Wallace's push for more cash to cover the cost of the war in Ukraine and soaring prices, amid fears the military has been 'cut to the bone'.

However, Chancellor Jeremy Hunt has been trying to beat the increase down as it scrambles to balance the books in the Budget next week. 

According to the Times, the increase to defence spending over the next two years is set to be £4billion-£5billion. 

Treasury officials are said to have pointed to existing ministry projects that are billions of pounds over budget.

Mr Wallace has also been embroiled in bitter clashes with veterans' minister Johnny Mercer. 

Mr Mercer said it was 'not credible' for Wallace to claim that the UK armed forces had been 'hollowed out', arguing that there had been significant rises in funding.

The Defence Secretary hit back that it was fortunate Mr Mercer was a 'junior minister' who didn't 'have to run a budget' and only had 12 people in his office.

Mr Mercer's wife, Felicity Cornelius-Mercer, waded into the spat by accusing Mr Wallace of behaving 'disdainfully'.

Mr Sunak, Mr Biden and Mr Albanese are expected to discuss their preferred submarine design for Australia's replacement fleet.

The Aukus security pact was struck in 2021 as a counter to Chinese activity in the Pacific.

It enraged Emmanuel Macron, as Australia cancelled a £47billion deal to buy 12 French diesel-electric submarines to enter the deal.

The number of British Army troops has been reduced from 83,000 in 2015 towards a target of 72,500 personnel by 2025. Army supplies have been depleted by the £2.3billion of military aid given to Ukraine last year. 

Former Armed Forces minister Mark Francois said: 'Given the brutal war in Ukraine, any increase in our defence budget is very welcome but we also need to reform our 'broken' procurement system, so that we can spend any extra resources more wisely – more cash by itself is not the answer.'

A series of parliamentary reports have laid bare the appalling state of some parts of the Armed Forces.

The MPs' defence committee found the military's armoured vehicle capability is 'obsolescent and outgunned', while the Public Accounts Committee said 'broken' military procurement practices resulted in billions of pounds of taxpayer money being wasted.

Former Tory leader Sir Iain Duncan Smith said: 'The Treasury shouldn't be playing games with this. There is a war going on and we are allies with the Ukrainians.

'The PM has already said we will do whatever it takes – but I'm afraid 'whatever it takes' is money.'