Thousands revel in the rain for the Queen's 90th birthday celebrations

Some 10,000 people were descending on the famous London thoroughfare, ahead of a carnival-style parade watched by the monarch, the Duke of Edinburgh, the Duke of Cambridge and Prince Harry.

As the gates opened for ticket holders at 10am, the first party-goers passed through security checks, ready to collect their wicker basket hampers.

With rain falling, many of the ticket holders were decked out in sheer white oversized ponchos handed out by the organisers.

Some wore union flag hats or carried patriotic flags as they moved down The Mall looking for their seats.

Among the first to collect their hampers were Maxine and Nigel Hawkins from Gloucester.

Mrs Hawkins, 53, said: “We’re going to find our seats and then hover under the trees.”

The couple received their tickets through the Gloucestershire and Warwickshire steam railway.

The Queen’s grandson Peter Phillips has masterminded the open air Patron’s Lunch to mark the monarch’s patronage of more than 600 charities and organisations.

It will bring to a close this weekend’s events marking the Queen’s anniversary that has already seen a St Paul’s Cathedral thanksgiving service and a traditional Trooping the Colour ceremony.

Heavy showers are forecast for later.

Tickets for the event were priced at £150 with the majority going to organisations or charities that have the Queen as patron and 2,500 sold to the general public.

Mr Phillips is a director of Sports and Entertainment Ltd, a global events agency which came up with the idea for the not-for-profit event and will receive an undisclosed fee for staging it.

The hampers were filled with a range of picnic lunch treats from a can of Pimm’s and a mini pork pie to two cupcakes.

The party will be shown live on big screens in St James’s Park and Green Park in London and will be televised on BBC One from 1.15pm.

The Queen and members of the family will later make an appearance to watch part of the colourful parade, before taking to a stage where William and Harry are expected to pay tribute to their grandmother.

The parade will have themes for each era of the Queen’s reign, kicking off with nautical-themed props and a giant puppet of the Royal Yacht Britannia.

A flower power theme will dominate the 1960s, while a 1980s “neon” vibe will feature Rubik’s cubes and leg warmers.

Some 1,600 volunteers from Patron’s organisations from across the UK and Commonwealth will take part and reflect a variety of categories including animals, the Armed Services, children and young people, arts and culture.

Each decade will be supported by 50 dancers from the Royal Academy of Dance, and accompanied by musical groups from within the Patron’s organisations and beyond.