Countdown's Carol Vorderman has been on the show since it started

Sir Alex Ferguson, Dame Julie Andrews and Lord Attenborough also recorded video messages for the programme.

The tributes will form part of a special 25th anniversary edition of the show to be screened on 2 November.

The teatime quiz was the first show to air on Channel 4 when it began broadcasting in 1982.

The Prime Minister says: "I want to congratulate Countdown on reaching 25 years on air. It's done more than any other programme to make counting and spelling fun and popular and is really good exercise for the mind."

Budget help

He also discloses that he could have done with the help of the programme's number cruncher Carol Vorderman when he was Chancellor.

"I wish she could have helped on some of my budgets when I was Chancellor - I might have got the sums right more often!"

Richard Whiteley presented Countdown for over 20 years

Dame Julie Andrews says in her tribute that the programme "has helped my spelling and math enormously".

Other well-wishers include Sir Terry Wogan, astronomer Sir Patrick Moore and stars of TV soaps Emmerdale and Coronation Street.

The 25th anniversary show will feature Conor Travers, who at the age of 14 became the youngest contestant to win the grand final of the TV quiz last year.

It will be preceded on Channel 4 by a replay of the first Countdown programme, which was aired on November 2 1982.

It was presented by original host Richard Whiteley, who died in June 2005.