The Defence Secretary has said there is a "real danger" President Vladimir Putin could "lash out" against Europe.
Speaking at the land warfare conference at Royal United Services Institute (RUSI), the defence and security think tank, Ben Wallace has said investment in defence spending must "continue to grow" to counter the threat of a resurgent Russia.
"If the threat changed so must the funding. If governments historically responded every time the NHS has a winter crisis so must they when the threats to the very security which underpins our way of life increases," he said.
"For too long defence has lived on a diet of smoke and mirrors, hollowed out formations and fantasy savings when in the last few years threats from states have started to increase," Mr Wallace said.
"Right now Russia is the most direct and pressing threat to Europe, to our allies and these shores.
"I am serious when I say there is a very real danger Russia will lash out against wider Europe. In these days of long-range missiles and stealth, distance is no protection."
He went on: "The threat is growing, is global and multidomain. It is now time to signal that the peace dividend is over and investment needs to continue to grow before it becomes too late to address the resurgent threat and the lessons learned in Ukraine.
"It is time to mobilise, be ready and be relevant."
The Defence Secretary has reportedly written to Boris Johnson calling for a 20% increase in defence spending to meet shortfalls in military capabilities.
A No 10 spokesman said: "In 2022, the PM announced the largest increase in defence spending since the Cold War. That cemented our position as the biggest defence spender in Europe.
"That was a £16.5bn increase over four years. That meant we could continue to provide crucial military support to Ukraine as well as allowing us to invest in a range of capabilities such as vehicles and drones and other areas of defence capability.
"Departmental spending on matters like that are for the Chancellor and are part of fiscal events. The Prime Minister has always said we would respond to any changes in terms of threat which is why we announced the extra funding for the Ministry of Defence."