Ukip has selected former Tory Roger Helmer as parliamentary candidate to fight the Newark byelection, despite him arguing date rape victims can bear some responsibility for being assaulted, coming out in favour of the death penalty and comparing gay marriage to allowing incest.

Roger Helmer, who was until two years ago Conservative MEP, will fight to win the Nottinghamshire seat vacated by the resignation of Patrick Mercer following a lobbying scandal. The Conservative candidate is former Christie's executive Robert Jenrick, while Labour has selected local councillor Michael Payne.

Helmer, 70, is a businessman who was elected to the European parliament in 1999 as a Conservative Party MEP and re-elected in 2004 and 2009 before defecting to Ukip in March 2012.

The senior Ukip politician is the party's spokesman on energy and has become its leading critic of windfarms and other green technology.

However, he has also aired controversial views on other subjects, including questioning the existence of homophobia, suggesting that some people find same-sex relationships "distasteful if not viscerally repugnant" and arguing that there are "different degrees of culpability" in rape cases.

Last year, Farage admitted that Helmer had gone too far by drawing a link between gay marriage and incest in a blog in which he wrote: "If two men have a right to marry, how can we deny the same right to two siblings? Are we to authorise incest?"

As a Tory MEP in 2011, Helmer was rebuked by his own party for sending out a tweet during a spate of riots suggesting that the army should "shoot looters and arsonists on sight".

Helmer, who has represented the East Midlands in the European parliament for 15 years, was "overwhelmingly" endorsed by the Newark constituency association at a hustings meeting on Monday before being backed by Ukip's national executive committee, said a party spokesman.

Helmer said: "I am both proud and humbled to have been selected by the constituency association in Newark to represent the Ukip cause in this historic town in what could well prove to be an historic byelection.

"It would be a huge honour to be elected to serve as Newark's MP and I will be giving my all over the next few weeks to achieve that outcome."

Farage said: "I had a feeling from pretty early on that Roger would emerge as the Ukip candidate in this contest. It did not surprise me in the slightest that he performed so well at the hustings or that NEC members were keen to endorse him.

"He is a massively experienced and respected figure on the national political stage and on the local political stage as well. I know that the Ukip membership will rally to the cause of making Roger our first directly-elected MP."