Britain must urgently enhance its defence capabilities by creating and training a "citizen army" ready to respond to future land-based conflicts,  according to General Sir Patrick Sanders, the outgoing Chief of the General Staff (CGS).

General Sanders, speaking at the International Armoured Vehicles conference in London, said the UK needed to expand its army size, currently around 74,000, to approximately 120,000 within three years. 

"We will not be immune and as the pre-war generation we must similarly prepare - and that is a whole-of-nation undertaking," he said.

"Ukraine brutally illustrates that regular armies start wars; citizen armies win them.

General Sanders clarified that his proposal is not an endorsement of conscription, instead a voluntary mobilisation of citizens should the need arise in times of war. The General, who has been critical of budget cuts and falling army numbers, stressed that merely augmenting reserve forces would fall short of addressing the multifaceted challenges presented by modern conflicts.

"Our friends in eastern and northern Europe, who feel the proximity of the Russian threat more acutely, are already acting prudently, laying the foundations for national mobilisation.

"As the chairman of the NATO military committee warned just last week, and as the Swedish government has done...taking preparatory steps to enable placing our societies on a war footing when needed are now not merely desirable but essential."

General Sir Roly Walker will take over as CGS in June with some media speculation that General Sanders, was being forced out of the role.

Concerns about army numbers are not new. General Lord Dannatt recently told The Times recently that the British army has fallen in size from 102,000 in 2006 to 74,000 today. That number is expected to fall below 70,000 in two years time.

Writing in The Times, General Dannatt compared the situation to the 1930s when the “woeful” state of the UK’s armed forces failed to deter Hitler.

“There is a serious danger of history repeating itself,” he said.