Britain would struggle to match Russian military capabilities on the battlefield and risks falling further behind potential adversaries without more investment, the British Army head will warn on 22 January.

In a rare public speech, Nick Carter, Chief of the General Staff (CGS) of the British Amy, is expected to say that Russia is building increasingly aggressive and expeditionary forces while it has already demonstrated the use of superior long-range missiles in Syria.

In 2017, Moscow also initiated simulated attacks across northern Europe, from Kaliningrad to Lithuania, Carter will outline in a speech at the Royal United Services Institute (RUSI) in London.

According to UK Ministry of Defence, Nick Carter is expected to say: ‘The time to address these threats is now -- we cannot afford to sit back.

‘Our ability to pre-empt or respond to threats will be eroded if we do not keep up with our adversaries. We must take notice of what is going on around us or our ability to take action will be massively constrained. Speed of decision making, speed of deployment and modern capability are essential if we wish to provide realistic deterrence.’

According to RUSI, the stark comments will be delivered in a speech focused on ‘the increasingly real threats that pose a risk to the UK's way of life.’

They come as years of austerity and public sector funding cuts have left Britain's armed forces strained and Philip Hammond, UK’s Finance Minister, is under pressure to act.

UK Defence minister Gavin Williamson, who only took over the role in November after his predecessor Michael Fallon stepped down over a sexual harassment scandal, is reportedly calling for increased funding.

Carter's expected remarks will add to the pressure on Hammond to bow to those demands.

Nick Karter is expected to say: ‘State-based competition is now being employed in more novel and increasingly integrated ways and we must be ready to deal with them.

‘The threats we face are not thousands of miles away but are now on Europe's doorstep -- we have seen how cyber warfare can be both waged on the battlefield and to disrupt normal people's lives -- we in the UK are not immune from that.’

Carter's anticipated warning follows similar comments from retired defence chiefs in recent months.

Sir Richard Barrons, until last year the head of Britain's Joint Forces Command which prepares for future conflicts, called for the defence budget to be raised to ensure the UK armed forces could adequately protect against potential attacks from China or Russia.