The former Conservative Party chairman Lord Norman Tebbit has launched a foul-mouthed attack on David Cameron, claiming the prime minister has “fucked things up” over the Marriage (Same Sex Couples) Bill. He also suggested that brothers should be allowed to marry each other if gays can.

Yesterday, the bill risked being derailed and required the support of Labour MPs to overcome a potentially lethal wrecking amendment.

In an interview with the Big Issue magazine Lord Tebbit said ministers had alienated traditional Tory voters.

The party leadership “fucked things up,” Lord Tebbit remarked, adding that the UK Independence Party would pick up support as a result.

A new opinion poll last night put UKIP just two points behind the Conservatives.

Lord Tebbit said: ‘If [UKIP] make significant gains in the European elections, I know there’s people rich enough to get involved and fund a significant campaign at a general election.”

Discussing the impact of legalising equal marriage, Lord Tebbit suggested it be extended to family members.

He said: “It’s like one of my colleagues said: we’ve got to make these same-sex marriages available to all. It would lift my worries about inheritance tax because maybe I’d be allowed to marry my son. Why not?

“Why shouldn’t a mother marry her daughter? Why shouldn’t two elderly sisters living together marry each other? I quite fancy my brother!”

Lord Tebbit also questioned whether the reforms could cause chaos when combined with changes to the rules of succession.

“I said to a minister I know: “Have you thought this through? Because you’re doing the law of succession, too.”

Lord Tebbit said: “When we have a queen who is a lesbian and she marries another lady and then decides she would like to have a child and someone donates sperm and she gives birth to a child, is that child heir to the throne?”

Last month, Lord Tebbit told a PinkNews.co.uk reader that the ban on same-sex marriage is not discriminatory, but the current system of not allowing heterosexual couples to enter into a civil partnership is.

The Marriage (Same Sex Couples) Bill is to receive a third and final Commons reading throughout this afternoon and evening.