The charity Mencap welcomed the decision to give athletes with a learning disability a chance to fulfil their Paralympic ambitions.
But it warned that if funding was not available immediately, athletes would not be ready to compete in the London 2012 Paralympic Games.
The International Paralympic Committee voted to allow athletes with an intellectual disability to participate in the event.
Athletes with learning disabilities have been banned since 2000, when the Spanish basketball team was revealed to have cheated at the Sydney Games.
Mencap called on the Government to ensure funding was available immediately so athletes were ready to compete.
Chief executive Mark Goldring said: "Everyone at Mencap is delighted that after years of campaigning, athletes with a learning disability will no longer be excluded from the Paralympic Games.
"However, without immediate funding, British athletes will remain excluded from London 2012 despite the ban being lifted. This would be a national embarrassment."
A spokeswoman said funding had been cut as a result of the ban, as elite sport funding was only available to elite athletes who would be medal hopefuls in Paralympic competition.
Before the ban, elite athletes with a learning disability qualified for lottery funding which is available to all world-class elite athletes, she added.
Minister for the Olympic and Paralympic Games Tessa Jowell said: "I very much welcome this and am delighted that athletes with intellectual disabilities will be competing in the 2012 Olympics."