Media playback is unsupported on your device Media caption Former Tory MP Patrick Mercer: "What's happened has happened, I'm ashamed of it"

A former Tory MP has resigned after he was suspended from the Commons for six months for allegedly asking questions in Parliament in return for money.

Patrick Mercer said he was "ashamed" and had decided to "fess up" by standing down straightaway.

This will trigger a by-election in his Newark constituency in Nottinghamshire, which he has represented since 2001.

The UKIP leader Nigel Farage has said he will decide in the next 24 hours whether to stand in the by-election.

Analysis A story about a former Conservative MP resigning in disgrace from the House of Commons, has almost immediately become one about UKIP. The prospect of its leader Nigel Farage contesting a high-profile Westminster by-election will cause alarm in Tory ranks. With opinion polls suggesting UKIP could come top in the European elections, Mr Farage will want to keep the momentum going. Last time round the party's support collapsed between Euro elections and the general election. It would be a very tall order for UKIP to overthrow the Tories in Newark. With a majority of more than 16,000, Patrick Mercer got more votes than all the other candidates put together. But historically by-elections have produced huge electoral swings and anything is possible. UKIP came from nowhere in the Eastleigh by-election in 2013 to take second place. Winning a Westminster seat is the big prize. The UKIP leader has reservations because he has no local connections with Newark, but he says a victory would completely transform his party's prospects. But those salivating at the prospect of a Nigel vs Boris contest look set to be disappointed. The Conservatives very quickly announced that Robert Jenrick had been selected as their candidate some time ago and he would be contesting the seat.

Mr Mercer was filmed by undercover reporters from the BBC's Panorama last year apparently agreeing to set up a parliamentary group to push for Fiji to return to the Commonwealth.

The MP had already said he would not contest the general election next year and had been serving as an independent since May 2013.

In a short statement, the former soldier said he would not contest the findings of a report into his conduct, to be published on Thursday, which will call for him to be barred from Parliament for six months.

He said he was resigning with "a great heaviness of heart" for the sake of his family and he hoped that his constituents would "tolerate" him in the future.

"I am an ex-soldier, I believe that when you have got something wrong, you have got to 'fess up and get on with it," he said.

"No point shilly-shallying or trying to avoid it. What has happened, has happened. I am ashamed of it. Therefore I am going to do what I can to put it right for the constituency of Newark."

The MP, a prominent critic of David Cameron who was sacked as a shadow minister in 2007, said that he hoped that his successor as MP for the constituency would be a Conservative.

BBC deputy political editor James Landale said a by-election would be a "huge headache" for the Conservatives, who have already chosen 32-year old Robert Jenrick, a lawyer and director of auction house Christie's, to fight the seat.

Although the Conservatives have a majority of 16,000 in Newark, the seat would be a prime target for UKIP at a time when it is soaring in the polls, he added.

By-election

UKIP leader Nigel Farage has said he will decide on Wednesday whether to stand in the by-election, the date of which will be decided in the coming days.

Image copyright The Conservative Party Image caption Robert Jenrick, pictured with his wife Michelle, has been selected to represent Newark for the Conservatives

He told the BBC that he was "tempted" to stand as winning a single seat in Westminster would "completely transform" the party's prospects, but had to consider whether it was the right opportunity.

Under parliamentary rules, a by-election cannot be held before the date of the European Parliament elections on 22 May, thus removing one potential obstacle to Mr Farage - who is seeking re-election as an MEP - putting his name forward.

Labour, which held Newark between 1997 and 2001, has already selected Michael Payne as its candidate.

Patrick Mercer Biography Born in 1956, the son of an Anglican clergyman who went on to become the Bishop of Exeter

Studied modern history at Oxford University and attended the Royal Military Academy at Sandhurst

Spent 25 years as an army officer, serving in Northern Ireland, Bosnia, Uganda and other countries, before working as a journalist

Elected as MP for Newark in 2001

Served as shadow minister for homeland security under Iain Duncan Smith, Michael Howard and David Cameron, before Mr Cameron fired him in 2007 after a row over alleged racist comments

The standards committee of MPs met on Tuesday to discuss Mr Mercer's case and its decision was reported by The Week magazine on Tuesday afternoon. A Westminster source has confirmed to the BBC that the report of a six-month sanction is correct.

Mr Mercer resigned the Tory whip last year after a report by BBC's Panorama claimed that he broke Parliament's lobbying rules by accepting £4,000 to lobby for business interests in Fiji.

BBC One's Panorama alleged that he had submitted five parliamentary questions in relation to his paid work as a lobbyist for a fake company that the programme had set up, in conjunction with the Daily Telegraph.

Parliamentary rules prohibit MPs from accepting money "to ask a parliamentary question, table a motion, introduce a bill, table an amendment to a motion or a bill, or urge colleagues or ministers to do so".

At the time, Mr Mercer said he took the money for consultancy work outside Parliament but referred himself to Parliament's standards watchdog.