Activist Peter Tatchell has written an open letter to Olympic bosses urging them to make a stand for gay rights by banning homophobic countries from competing in the games.
In an open letter to Olympic chiefs Jacques Rogge and Lord Coe, Tatchell calls on participating countries which are known to discriminate against lesbian, gay, bisexual and transgender people to sign a pledge supporting equal rights or be disqualified from the sporting event.
He also urges the International Olympic Committee (IOC) and the London Organising Committee of the Olympic and Paralympic Games (LOCOG) to make a public statement welcoming LGBT athletes and that anti-gay participating nations must not discriminate on the grounds of sexual orientation and gender identity.
Tatchell claims over 150 nations have anti-LGBT policies and their involvement in the games goes against the Olympic Charter which states that any discrimination is 'incompatible' with the Olympic spirit.
'The Olympics should be open to everyone, based solely on merit and without discrimination,' Tatchell wrote.
'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.'
In the letter, the renowned gay rights campaigner singles out participating countries which he claims clearly 'violate the Olympic spirit of equality', including Saudi Arabia, Iran and India.
'Despite this laudable commitment, many nations deny equal opportunities to women and to ethnic, religious and sexual minorities,' he wrote.
Tatchell added: 'This discrimination takes the form of a lack of equal access to sports facilities, competitions and the Olympic selection process.'
The Olympic charter states that 'the practice of sport is a human right'.
It adds: 'Every individual must have the possibility of practising sport, without discrimination of any kind and in the Olympic spirit, which requires mutual understanding with a spirit of friendship, solidarity and fair play.'
The charter also says that any form of discrimination, including on the grounds of 'gender or otherwise' is 'incompatible' with the Olympics.
The opening ceremony for the London 2012 Olympic Games will be held on 27 July.