“Evidence is pretty clear” that Russia is planning an invasion of Ukraine, the British Prime Minister Boris Johnson said on Monday.

And he would recall parliament if the invasion does go ahead so that MPs can unite and agree the toughest possible sanctions against Russia.

Potentially, that would be very damaging to Russia which has heavy exposure to the City of London. Plus, many of Vladimir Putin’s closest allies have invested a great deal of their wealth in the UK.

On a visit to Scotland on Monday, Boris said there were Russian troops massing on the Ukrainian border and “all sorts of other signs that show that there are serious preparations” going on.

He called it “a very, very dangerous, difficult situation” but said “there is still time for President Putin to step back”.

He called for more dialogue and urged Russia to avoid a “disastrous” invasion.

Boris was meant to stay overnight in Cumbria but those arrangements were called as he rushed back to 10 Downing Street.

The Prime Minister, who received a security briefing from his intelligence chiefs on Monday, will chair a meeting of the government’s “Cobra” emergency committee on Tuesday.

Asked if he agreed with the claims by Ben Wallace that there was a “whiff of Munich” and appeasement in actions against President Putin so far, Boris said that his defence secretary was “absolutely right to say it’s very important that we’ve got to be strong, and we’ve got to be resolute and we’ve got to be united”.

He said it was particularly important to present a united front when it came to economic sanctions.

“The UK, as you know, has been in the lead in bringing our allies together so that there’s a tough package of sanctions,” he pointed out. “It’s very, very important that the West should stand united, particularly that Nato has done it.

“It’s been pretty encouraging to see the way countries have pulled together.” The Labour leader, Keir Starmer, who was in Sunderland in northeast England on Monday, is pressing for the toughest possible sanctions.

He said: “I’d like that threat (of sanctions) to be very real because let’s see this for what it is. It’s Russian aggression. So, I would say to the Government go further on sanctions.”

He went on: “Russia wants to see our allies divided, it wants to see division in the United Kingdom, and we are not going to divide and, therefore, we support the government in what it’s doing.”

He, too, wanted Parliament, now in recess, to be recalled if Russia invaded Ukraine because there must be “a swift and strong” response from the UK, and “a united response with our allies”.

The sanctions should include targeting a broader range of individuals and businesses, Starmer said.