The BBC has apologised after Tory donor and Pimlico Plumbers boss Charlie Mullins used a radio interview to call Jeremy Corbyn a "twat" for supporting Britain's withdrawal from the European single market.
Mr Mullins was asked by BBC Radio 4 World At One host Martha Kearney whether the UK should be seeking to remain in the trade bloc after Brexit.
He replied: "Course we should be staying in, Jeremy Corbyn's a t*** ain't he?"
The presenter then intervened: "Well we'll definitely leave it there.
"Apologies to Jeremy Corbyn for the language used."
Mr Corbyn is currently resisting pressure from some in Labour to change party policy to back staying in the single market.
Mr Mullins, whose company has donated more than £48,000 to the Tories since 2015, spoke after commenting on a Supreme Court ruling which prompted the Government to take immediate steps to stop charging employment tribunal fees.
Pimlico Plumbers lost a separate Court of Appeal case on workers' rights in February against a plumber who successfully challenged the company's view that he was self-employed at an employment tribunal.
It was viewed as a victory for campaigns to win rights for the growing army of self-employed workers and came amid ongoing concern about the so-called "gig economy".
Mr Corbyn said earlier this month: "We've got to get rid of the gig economy and bogus self-employment."
Commenting on Mr Mullins' radio outburst, a Labour source said: "Jeremy condemns all, and does not engage in any, personal abuse."