Three councillors who quit the Tories to join the UK Independence Party (UKIP) should take advantage of an upcoming by-election by winning a new mandate from the public, Wimbledon's MP has urged.

A by-election was announced for Colliers Wood ward on Friday following the recent death of Labour Councillor Gam Gurung, who battled with cancer for six months.

With an election set to take place on Thursday, August 8, Stephen Hammond MP has challenged his former Merton Conservative Councillors Suzanne Evans (Hillside ward, Wimbledon), Richard Hilton (Lower Morden ward) and Rod Scott (Raynes Park ward).

Mr Hammon said they should resign and fight a byelection as UKIP councillors, believing it would be timely, cost-effective and give residents a say on whether they want to be represented by UKIP.

All three Conservative councillors resigned from the party in spectacular fashion during a full Merton Council meeting in April, citing a "poisonous war" among their former colleagues which had forced their hand - and later defected to UKIP.

Mr Hammond said: "I think it is time that Councillor Evans, Hilton and Scott put their money where their mouths are and resign to give themselves a clear indication if their defection is supported by their constituents.

"They have no current mandate to serve and should resign - I issue this challenge today.

"I have written to the three councillors with this challenge and I await to see if they have the courage to take up this invitation to behave honourably."

A spokesman for Merton Council said that each single by-election costs £13,000 and, while "about £1,000" could be saved in printing costs should all four by-elections take place at the same time, the additional cost would still be in the region of £35,000.

The three Merton Conservative councillors who defected to UKIP in May said the Wimbledon MP "must be joking" in response to calls for them to stand down.

Coun Evans, leader of Merton’s UKIP, has previously said calling a by-election would be a waste of public money given that another election has to be held in June 2014, when all 60 councillors will be chosen to represent Merton for four years.

Coun Evans said: "If we had defected from the Labour Party to the Conservatives, Stephen Hammond would be welcoming us with open arms and slapping down any cries of ‘foul play’ from Labour.

"As he hass frequently praised my work as a councillor in the past, and criticised my Conservative ward colleagues, I think he’s got some cheek."

Coun Hilton said: "We made it clear, through the pages of this paper and others, that if 20 per cent of our electorate called for a by-election within six weeks of our defection then we would naturally stand down and force one - this hasn’t happened.

"Meanwhile, the three of us have had significant numbers of people tell us they will never vote for Stephen Hammond again after his calls for MPs to have to £40,000 pay rise and because of his vote for gay marriage."

Coun Scott said: "We will continue to represent our constituents to the best of our abilities as we have always done, and we will listen to those who elected us, in a way the Conservatives have never done."

"UKIP will be facing the electorate across Merton soon enough, and in Colliers Wood within the next few weeks, and we relish the challenge."