A Labour candidate for the next election has been threatened with a libel action by the MP whose Norwich South seat he is trying to win.

Liberal Democrat Simon Wright, who won the seat from Charles Clarke in 2010, has warned Clive Lewis he will take legal action if he does not retract claims that he had voted to treble tuition fees in a canvassing email.

It is not known how many people saw the claim, but the Lib Dem member is demanding an immediate apology.

Mr Lewis last night issued a statement to clarify his stance, but stopped short of a full expression of regret, hitting out at the Liberal Democrat U-turn on higher education.

He said: 'I am happy to clarify that Simon Wright did not himself vote to raise fees. However, before the last General Election, the Liberal Democrats promised the electorate they would not raise tuition fees – a promise that they shamefully broke as part of their grubby coalition deal with the Tories.

'However, the simple fact remains that Simon Wright's Lib Dem pals in parliament broke their promise to not raise tuition fees, letting down students and families across the country, including thousands here in Norwich.'

Goodman Derrick Solicitors, acting on behalf of Mr Wright, has sent a letter to Mr Lewis stating that although his publication referred to the 'Liberal Democrat MP for Norwich South' it was an 'obvious reference' to the man they are representing. Mr Lewis, a former journalist who still works for the BBC, has been told that to avoid legal action a number of criteria must be met.

They include a written apology, a disclosure of the number of people who saw the alleged defamation, the sending of a prominent correction, and the payment of more than £400 in legal costs.

Mr Wright said: 'I'm very disappointed that my Labour opponent has chosen to issue a statement that is so clearly untrue. The truth is a matter of public record and was widely reported by local and national media at the time. I voted against increasing tuition fees. Mr Lewis has been made aware of his error but so far has failed to explain or retract his untrue claims. It is time for him to set the record straight and to commit to checking his facts in the future.'

Four years ago pressure mounted on Mr Wright to honour a pledge he made to the National Union of Students (NUS) to oppose any increase in tuition fees. After coming under intense scrutiny and criticism he finally voted against the government's plans.