Tens of thousands of people are pouring into Brighton and Hove today for Pride 2003.

The festival will turn the city into an explosion of music and colour as the crowds take part in Britain's leading lesbian, gay, bisexual and transgendered event.

A parade, including 40 floats, marching bands and a sea of partygoers in flamboyant costumes, will make its way through the city to Preston Park.

The theme is The Greatest Show On Earth, based loosely on Cecil B DeMille's 1952 movie of the same name in which Betty Hutton, Dorothy Lamour, James Stewart and Charlton Heston act out their dramas under the Big Top.

This year, for the first time, there will be a circus in Preston Park.

Other attractions include a cabaret tent, women's tent, dance tent, funfair, food outlets and shopping village.

The procession starts at Madeira Drive at 11am and the first floats are expected to arrive at the park at about 12.30pm.

From modest beginnings, Brighton and Hove's annual festival has grown into a major event, drawing crowds from all over Britain and abroad.

While similar events have floundered or become fee-paying, Pride in Brighton and Hove has remained free and, fostered close links with the wider community.

It has also become more than just a one-day celebration, with events taking place all year round. This year there has been a day at the races and a dog show.

The festival is organised by the voluntary Pride in Brighton and Hove committee, which has worked throughout the year to ensure today's event goes ahead.

The committee's success in preparing the way for the biggest show in the event's history has attracted attention from political leaders.

Prime Minister Tony Blair offered his best wishes to everyone at the event, adding: "I would like to pay tribute to the organisers who work so hard on this celebration of diversity and the breaking down of barriers of prejudice and discrimination within our society."

Conservative leader Iain Duncan Smith said: "I am delighted to send my best wishes to all those attending Brighton and Hove Pride 2003 and I am sure the hard work of all those involved in planning the parade and the party afterwards will make it an enjoyable occasion."

Lib Dem leader Charles Kennedy said: "Events such as Pride are not only important as a celebration but also help to raise awareness of the lesbian, gay, bisexual and transgendered communities all over Britain.

"I hope everyone has a wonderful day."

David Panter, chief executive of Brighton and Hove City Council, said: "This is a marvellous event, clearly one of the high-points of the summer season.

"Pride was originally brought about by the lesbian, gay, bisexual and transgendered community and now has a central place in Brighton and Hove's summer events programme.

"It is an event that is enjoyed by people all over the city."

Sue John, deputy leader of Brighton and Hove City Council, added: "Pride has become such an integral part of the city's round of festivals, it would be impossible to imagine the city without it."

"It is a credit to the organisers who, year on year, manage to stage an immensely colourful, lively, and joyful event."

Madeira Drive was due to be closed between the Aquarium roundabout and Peter Pan's Playground from 6am to noon today for the parade.

Motorists will be diverted away from London Road to allow the procession to work its way to Preston Park.

The council said several other roads would be closed for street parties during the weekend.

Pavilion Street was due to shut today and closures have been announced tomorrow at Brewer Street, St Martin's Street, Rock Place and parts of St James's Street at different times during the day.