Washington has already banned US individuals from any financial dealings with the breakaway territories in Ukraine.

The White House said the sanctions were not the same draconian measures, including crippling Russia’s banking sector, that it has threatened if Russia actually launched an invasion.

Britain’s harshest measures enable the government to slap Russian oligarchs close to President Putin with asset freezes and travel bans in a toughening of UK sanctions laws.

Mr Johnson announced five Russian banks and three high net worth individuals would be sanctioned by Britain.

“Now the UK and our allies will begin to impose the sanctions on Russia we have already prepared,” he told the Commons

“Today the UK is sanctioning the following five Russian banks: Rossiya, Jenn Bank, General Bank, Promsvyazbank and the Black Sea Bank.”

“We are also sanctioning three very high net worth individuals: Boris Rotenberg, Igor Rotenberg and Gennady Timchenko. Any assets they hold in the UK will be frozen, the individuals concerned will be banned from travelling here and we will prohibit all UK individuals and entities from having any dealings with them.”

“This is the first tranche, the first barrage. We hold further sanctions,” he added.

However, Sergei Lavrov, Russia’s veteran foreign minister, has dismissed the threat of Western sanctions.

He said: “Our European, American, British colleagues will not stop and will not calm down until they have exhausted all their possibilities for the so-called ‘punishment of Russia’. They are already threatening us with all manner of sanctions or, as they say now, ‘the mother of all sanctions’.”