Human rights campaigner Peter Tatchell has renewed calls for Olympic chiefs to ban anti-gay nations from the London Games and enforce the Olympic Charter by offering visiting nations the chance to renounce discrimination.

An open letter to Jacques Rogge and Lord Coe published today suggests an ultimatum be put to participating states at the Games of the XXX Olympiad.

Mr Tatchell said those which discriminate against lesbian, gay, bisexual and transgender people should either renounce such discrimination or be disqualified from the Games.

The International Olympic Committee and the London Organising Committee of the Olympic and Paralympic Games should, he writes, publicly welcome LGBT athletes.

The Olympic Charter states: “Any form of discrimination with regard to a country or a person on grounds of race, religion, politics, gender or otherwise is incompatible with belonging to the Olympic Movement.”

Mr Tatchell writes that 150 nations are in violation of that Charter by discriminating against their citizens on the grounds of sexual orientation and gender identity.

Saudi Arabia, he says, “provides almost no sports facilities for women” and has provided two “token” female athletes for the Games.

Iran “practices systematic discrimination against its Kurdish, Arab and Baluch citizens. It holds gender segregated sports competitions and forces female competitors to cover themselves head-to-toe, even if they do not want to.”

In the absence of laws against anti-gay discrimination, he writes, “victimisation and bias against LGBT athletes is endemic in most competing nations”.

“This social marginalisation and exclusion means that in many countries women and minorities have almost no chance of representing their country at London 2012, no matter how talented they are. “

He said: “The Olympics should be open to everyone, based solely on merit and without discrimination.

“Sport should have no boundaries or exclusions. There should be a level-playing field for all competitors, regardless of their background.

“Any country that discriminates against women or ethnic, religious or sexual minorities should be disqualified from the 2012 Olympics.”

The London 2012 Summer Olympics will run from 27 July to 12 August.