An American tabloid newspaper has alleged that the Republican party’s nominee for Vice President had an extra-marital affair.

It is the latest rumour about Sarah Palin, Governor of Alaska, who has already been forced to reveal her 17-year-old daughter is pregnant and faced questions about her links to Alaskan independence groups.

Republican Presidential candidate John McCain’s campaign called the National Enquirer story a smear and said they are considering legal action.

The paper claimed today:

“The National Enquirer’s coverage of a vicious war within Sarah Palin’s extended family includes several newsworthy revelations, including the resulting incredible charge of an affair plus details of family strife when the Governor’s daughter revealed her pregnancy.

“Following our John Edwards exclusives, our political reporting has obviously proven to be more detail-oriented than the McCain campaign’s vetting process.

“Despite the McCain camp’s attempts to control press coverage they find unfavourable, The Enquirer will continue to pursue news on both sides of the political spectrum.”

The Enquirer was reporting that former Democratic Presidential candidate John Edwards had fathered a child by his mistress for weeks before the rest of the American press picked the story up.

McCain campaign adviser Steve Schmidt said:

“The smearing of the Palin family must end. The allegations contained on the cover of the National Enquirer insinuating that Governor Palin had an extramarital affair are categorically false. It is a vicious lie.

“The efforts of the media and tabloids to destroy this fine and accomplished public servant are a disgrace. The American people will reject it.

“Legal action will be considered with regard to this disgraceful smear.”

The Governor’s 17-year-old daughter Bristol Palin is thought to be five months pregnant.

Politics blogs in America had been full of conspiracy theories that Bristol was in fact the mother of Governor Palin’s fifth child, who was born in April and has Down’s Syndrome.

While that rumour has been scotched, the Alaskan’s reputation among some Christian conservatives may suffer, and her strong support for abstinence-only sex education in schools has been called into question.

The former small town mayor would become the first woman to take office as Vice President if elected.

Governor Palin, 44, is three years younger than Barack Obama, who accepted the Democratic party’s nomination last week, and 28 years younger than Senator McCain.

She was elected Governor of Alaska less than two years ago. Her husband Todd is a Yup’ik Alaskan native.

The eldest of her five children, 18-year-old Track, is due to begin his military service in Iraq next month.

Her image as a hunting, shooting, snowmobile-riding outdoors woman helped boost her popularity in Alaska.

Governor Palin opposes abortion rights and supports the death penalty and Alaska’s ban on gay marriage.