Boris Johnson is a “fopdoodle” and Theresa May is trying to dodge scrutiny by refusing to take part in TV debates or meet undecided voters, Labour's deputy leader has claimed.

Tom Watson hit back at the Foreign Secretary in colourful language after Mr Johnson's attack on Jeremy Corbyn last week, branding the Tory “cack-handed” and “cheese-headed”.

He also compared the Prime Minister to a robot over her slogan-heavy media appearances on the General Election campaign trail.

The Foreign Secretary branded the Labour leader a “mutton-headed old mugwump” who would be a threat to national security.

In response, Mr Watson said: “Boris Johnson is a cack-handed, cheese-headed fopdoodle, with a talent for slummocking about, who would do less damage to Britain's reputation in the world if Theresa May sacked him as Foreign Secretary and replaced him with a souvenir paperweight.

“When we require diplomacy, Boris Johnson sows discord. At a time when we need a serious-minded national representative to deal skilfully with some of the most complex problems our country faces, Boris Johnson falls back on bluster.

“And how can any of us trust a man who claimed our NHS would get an extra £350 million a week if we left the EU?”

The Labour deputy leader mocked Mrs May's carefully staged campaign appearances in front of Tory loyalists, rather than members of the public.

“She isn't just trying to avoid scrutiny in the House of Commons, she's trying to dodge scrutiny on the campaign trail too,” he told the Usdaw union's annual conference in Blackpool.

“Refusing a TV debate against Jeremy Corbyn and the other party leaders. Visiting a workplace in Leeds - but only once all the actual workers have packed up and gone home for the night.

“Filmed on the campaign trail in Wales - but only speaking to Conservative Party activists, not members of the public.

“And on the few occasions she does let someone ask her a question, just repeating the same words over and over again.

“A lot of people are worried about the risk of robots taking their jobs. I fear with this Prime Minister it's already happened.”

Mr Watson, who has clashed with Labour leader Mr Corbyn in the past, acknowledged the internal difficulties his party has endured, telling the shopworkers' union: “We should never see abuse or intimidation as just another part of the job.

“I didn't need to spend two years as Labour's deputy leader to understand that... although it certainly helped.”

He claimed that Mrs May's U-turn over calling an early election showed the Conservatives could not be trusted.

“Theresa May was meant to be the Tory leader who tells it like it is.

“A safe pair of hands. Someone to steady the ship. A Prime Minister who puts the country's interests above those of her own party.

“Now she's been exposed for what she really is: a political opportunist who's called an election she said she wouldn't have because she thinks she can increase her narrow majority in Parliament.

“We need to make her regret that decision.”