Russia under President Vladimir Putin is potentially the “single greatest threat” to Britain's security, Foreign Secretary Philip Hammond has warned.

In some of the strongest comments by ministers since the crisis in Ukraine, Mr Hammond said the Russian leader had decisively rejected efforts to draw his country into a “rules-based’ international order and was now actively seeking to subvert it.

He said that in the face of the “increasingly aggressive” stance of the Russian military, the effort to establish its intentions was now once again a “vital” element of the work of Britain's intelligence agencies – MI5, MI6 and GCHQ.

“The rapid pace with which Russia is seeking to modernise her military forces and weapons, combined with the increasingly aggressive stance of the Russian military, including Russian aircraft around the sovereign airspace of Nato states, are all significant causes of concern,” he said at the Royal United Services Institute in London.

It is no coincidence that all of our agencies are recruiting Russian speakers again

“We are in familiar territory for anyone over the age of about 50, with Russia’s behaviour a stark reminder that it has the potential to pose the single greatest threat to our security.

“Hence, continuing to gather intelligence on Russia’s capabilities and intentions will remain a vital part of intelligence effort for the foreseeable future. It is no coincidence that all of our agencies are recruiting Russian speakers again.”

His comments come after Defence Secretary Michael Fallon warned last month that there was a “real and present danger” that Mr Putin could try to de-stabilise the Baltic states – Latvia, Lithuania and Estonia – which, unlike Ukraine, are all members of Nato.