General Sir Nicholas Carter, Chief of the General Staff, will issue the worrying warning that the UK is in real trouble of not being able to respond to threats having neglected skills and equipment to counter hi-tech, capable armies.

In a speech at the Royal United Service Institute today, he will 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.”

The UK currently spends more on defence than any other European nation, paying out £36billion last year compared to France’s £32billion.

It pales in comparison to Russian spending that is believed to be about £50billion a year and army chiefs are worried about Russian dominance in areas including artillery, electronic warfare and cyber skills.

Sir Nick will continue: “The time to address these threats is now – we cannot afford to sit back.”

The Defence Secretary Gavin Williamson, along with a cross-party group of backbench MPS, has argued that any further cuts to the Army or Royal Navy would prove to be disastrous to Britain’s military might.

Prime Minister Theresa May is expected to order a national security and defence review to be split in two - the security element proceeding as planned but the defence section put back by months.

Sir Nick will add: “Our ability to pre-empt or respond to threats will be eroded if we don’t keep up with our adversaries.”

Since taking over from Sir Michael Fallon in November, Mr Williamson has fought on behalf of the Armed Forces and engaged in a row with the Chancellor Philip Hammond over spending.

Mr Williamson has already banned Mr Hammond from using RAF aircraft until he has paid his bills for previous flights.

It was claimed last month that Mr Hammond had told Mrs May the Army only needed 50,000 soldiers, 28,000 fewer than it currently has.

While the UK meets Nato’s target of spending two percent of national income on defence the Ministry of Defence faces a massive shortfall of £20-30 billion in its budget over the next decade if it wants to meet its commitments to build new warships, aircraft, submarines and vehicles.

When a Strategic Defence and Security Review was carried out in 2015, the MoD said it would cut its civilian personnel from 56,860 to 41,000 by 2020, but figures released earlier this year showed that it still had 56,690 civilian staff, meaning it had only cut 170 posts, rather than the 16,000 it had promised.

The MoD has said it “remains committed” to reducing civilian numbers by 30 per cent in the next two years, and fulfilling that promise will be one of Mr Williamson’s most urgent tasks.

It follows calls by Lord Ricketts, a former UK national security adviser and ambassador to France, who warned Paris and London will have to work harder to maintain their relationship once Britain frees itself from the clutches of Brussels.

He said: “Brexit will not weaken the case for close UK-French defence and security cooperation but it will change the context and create the risk of the two countries drifting apart.”

The peer, who has also served as a UK representative to Nato, acknowledged France and the UK have upped their commitment to cooperation on counter-terror and cyber-security initiatives in recent years “in response to recent terrorist attacks.

He added: “It is crucial that Brexit does not adversely affect this”

Lord Ricketts went on to warn the relationship was more vital than ever before in the face of “a more aggressive Russia, the emergence of North Korea as a nuclear power and the uncertainties about the longer-term US commitment to Nato following President Trump’s hesitations over re-affirming article 5”.