THE public will be called up to fight if the UK goes to war, the head of the British Army is set to warn.

General Patrick Sanders is set to announce in a speech today (January 24) that the military is its smallest size in centuries, and will urge the UK Government to “mobilise the nation” if a war were to erupt with Putin’s Russia – according to The Telegraph.

The newspaper understands that the army chief doesn’t support conscription, but rather a “change in mindset” whereby the UK public is prepared for an all-out war.

It came after Shapps last week made the case for increased western defence spending, saying the UK was facing a “pre-war world”.

READ MORE: Defence speech by Grant Shapps was based on a chilling assumption

In a major speech, he set out the risks posed by countries including China, Russia, Iran and North Korea as well as terrorist groups in an increasingly dangerous world.

Before taking on the defence brief, Shapps had backed a level of spending in excess of the Government’s goal, arguing it should rise to 3%.

He said in his Lancaster House address that the UK has increased its funding, with a record £50 billion a year being spent on defence.

But the speech was viewed as a push for extra funding, both at home and by Nato allies, many of whom are not meeting the alliance’s 2% of GDP spending target.

The National: The shrinking size of the British Army has been a source of political argument in recent month (Ben Birchall/PA)

Also last week, counter-terrorism police said Britain faced its most “acute threat” of hostile foreign interference and spying since the Cold War because of the “triple threat” of Russia, China and Iran.

And a former chief of the general staff of the British Army warned the UK risked a repeat of the 1930s unless more was invested in its armed forces.

General Lord Dannatt hit out at the shrinking size of the army, which he said had fallen from 102,000 in 2006 to 74,000 today “and falling fast”.

He drew parallels with the 1930s when the “woeful” state of the UK’s armed forces failed to deter Hitler, saying there was “a serious danger of history repeating itself”.

But Shapps insisted the size of the army would not dip below 73,000 under the Tories.

He said: “It’s not projected to go down to 50,000.

“It’s actually, specifically, to 73,000 plus the reserves.”

The senior Tory went on to play down concerns about the capabilities of the British military.