The former UKIP candidate for Clacton who was dropped by the party in favour of former Conservative MP Douglas Carswell is backing the Liberal Democrats on Thursday.

Roger Lord was to represent UKIP in next year’s general election in Clacton until Mr Carswell’s shock defection at the end of August.

Mr Lord was so angry at his treatment by the party and its leader Nigel Farage – whom he had considered a friend – that he resigned as a member of Essex County Council.

The replacement for his Brightlingsea county council seat is being chosen on Thursday – the same day as the parliamentary by-election – and Mr Lord is backing Liberal Democrat Gary Scott who finished runner-up to him in the seat in May 2013.

The news comes as former Foreign Secretary William Hague is due to arrive in the constituency to boost Tory campaigners hoping to see Giles Watling elected in the parliamentary by-election.

Mr Lord has also launched an attack on his group at the county. He said: “At County Hall I found that I was undermined by my own UKIP colleagues on issues such as the future of Meals on Wheels which were prevented from being debated.”

His letter says: “I am sure many people were surprised to hear that I have endorsed Gary Scott for the forthcoming county council by-election.

“The reality is that in order to achieve anything in local politics, a degree of co-operation and support from a variety of people is essential.”

Mr Scott told activists at his party conference in Glasgow about the letter.

In a rallying call for help from the party faithful at the Eastern region reception, he said Mr Lord had been “disgracefully” sidelined, when Mr Carswell decided to defect.

He said: “He (Mr Lord) was so upset he resigned his county council seat and he sent me an e-mail with a supporting letter, which we have used, printed on purple paper.

“It is being sent out to UKIP and Conservative supporters. We are determined. Roger Lord is going to vote for me. And hopefully his people in his part of the world. We have a great opportunity to take a seat off UKIP.

“If UKIP win the Clacton by-election they are going to say UKIP won it, but there will be a footnote that the Liberal Democrats took a seat from UKIP at the county council elections.”

Mr Scott added: “If we win we will become the main opposition and we can give the Conservatives so much grief.”

A Tory spokesman said: “First UKIP force out Roger Lord, their local democratically chosen candidate to contest the Clacton constituency, so Douglas Carswell could be parachuted in. And now we find out Mr Lord was also undermined by his own colleagues on the council.

“It’s even clearer that UKIP don’t care about Clacton and are only interested in getting national media attention.

They have no plan to help local hardworking taxpayers and would take our area backwards.”

No one from the UKIP campaign team wanted to comment on Mr Lord’s decision to back the LibDems in the council by-election.