Vince Cable has likened Theresa May to a school headteacher “barricaded in her own office” as he predicted the unfolding internal unrest within the Conservative party could boost the Liberal Democrats.

The Lib Dem leader, who is to address his party conference in Bournemouth later on Monday, was scathing about the prime minister’s apparent inability to discipline Boris Johnson after the foreign secretary’s personal manoeuvres over Brexit.

“If I was in charge of the government I’d fire the guy instantly,” Cable told BBC1’s Breakfast programme. “It just is a reflection of the extreme weakness of the prime minister’s position that she doesn’t seem prepared to do it.”

He continued: “It’s a bit like a school where discipline has broken down completely, the headteacher is barricaded in her own office, unwilling to impose discipline.”

Cable was similarly dismissive of Johnson himself, who was robustly criticised by Sir David Norgrove, head of the UK Statistics Authority, for repeating the claim that Britain could take back £350m a week in potential spending after Brexit.

“The problem with Boris Johnson’s statement is not that he’s arguing with other politicians only, he’s directly being contradicted by a very senior, respected public servant who’s got nothing to do with politics,” Cable said.

“His authority and credibility is just being completely shot to pieces.”

Asked whether, with only 12 MPs the Lib Dems could realistically take power at the next election, Cable argued that with politics in an “extraordinary state of flux”, this remained possible.

He said: “You’ve got the governing party, the Conservatives, more or less in open civil war, as we’ve seen this morning. You’ve got the Labour party in suppressed civil war. You’ve got extreme polarisation – hard right on one side, hard left on the other.



“I think there is an appetite in the country for moderate, common sense, middle-of-the-road politics, and that’s the kind of thing the Liberal Democrats represent.”

He added: “I think the public will warm to us. We could break through – we’ve seen this in other western democracies.

“If the Conservative party continue to disintegrate with this infighting that we’re seeing at the moment over Europe, and if the Labour party’s civil war reignites, all kind of changes are possible. I’m there, we’re there as a party to take up the reins for the millions and millions of people in this country who want competent, middle-of-the-road, sensible government.”

Asked about the party’s proposal for a new referendum on Brexit, Cable argued that this would not be a rerun of last year’s vote but a “first referendum on the facts, once we know the outcome of the referendum”.

He said: “The public should resolve this and have a choice – do they want to press ahead with the result of what the government has achieved, good or bad, or do they want an exit from Brexit? I think it’s the only way of resolving this issue and giving the country a stable, long-term future.”

Also due to speak at the Lib Dem conference on Monday was the party’s former leader, Tim Farron, who was to argue that his tactics “saved the Liberal Democrats”, saying the party’s increasing membership was a sign it was on the road to recovery.

Farron, who was succeeded by Cable, was to say: “The day I took over as leader, one journalist predicted confidently that ‘the party that began with Gladstone will now end with Farron’.

“I saw those assumptions that we were dead and buried and I resolved that we were going to survive, grow and win again. The Liberal movement of Gladstone, Lloyd George, Shirley Williams, Jo Grimond and Charles Kennedy – the movement I joined as a 16-year-old, was not going to die on my watch.”