The former Conservative MP claimed only a handful of people knew about the letter.
In a Newsnight interview, Natasha Bolter accused Roger Bird, Ukip's general secretary of 'lying' about the nature of their relationship.
Ukip general secretary Roger Bird claims he and Natasha Bolter had a sexual fling.
The British Election Study says the damage to Labour's core support has already been done.
Ukip launch 'full investigation' into claims relating to candidate selection.
The Ukip leader made 'absurd' excuse ahead of the party's first Welsh conference.
Diversity campaigners say Farage wrong to pick out Muslims.
'Patronising' poster condemned by Ukip MEP David Coburn
Ukip initially announced scrapping sex and relationship education for children under the age of 11.
Has Ukip made a glaring omission over white van Christmas card?
Cameron's migrant curbs and Ukip's anti-immigration views mean the UK will lose out on global talent.
Cameron's mismanagement of the immigration issue has thrust EU relations further into the spotlight.
Cracks appearing in Ukip unity as party struggles with 'fruitcakes and loonies' again.
Prime Minister David Cameron will announce new measures later on 28 November.
Mariano Rajoy is trying to regain public trust after a minister resigned over kickback allegations.
Right wing MEPs say Lux Leaks scandal makes Juncker unfit for office.
Podemos is tearing up Spain's political establishment and each setback is turning into triumph.
David Cameron then did his best to make the Ukip MP's question about the NHS appear facile.
Lord Ashcroft poll also showed Ukip's support had increased ahead of the general election.
Deputy Prime Minister says Ukip represent 'politics of blame' and he criticises Emily Thornberry over tweet.
Voting for Nigel Farage's party can lose you friends.
Prime Minister on the war path after defeat for Conservatvies in Kent