The display gardens for the 99th Chelsea Flower show burst into full bloom in London on press viewing day, despite one of the driest winters and wettest springs in Britain for decades and a tough economic environment sweeping Europe.

Severe drought in the southeast English region that includes London has led to the imposition of water restrictions and Chelsea designers have responded by making responsible water use one of the show's key themes.

Caroline Spelman, the British secretary of state for the Department of Rural Affairs and Food and a keen gardener, visited the Climate Calm garden, an installation that showed the effects of climate change in the water-stressed southeast.

"I feel I've learned a lesson as a gardener for this year and for all future years, which is to think carefully when I'm making choices about which plants use water sparingly, so that I too can use water wisely," she told Reuters.

The show, which takes place on the sprawling lawns between the red-bricked elegance of the Royal Hospital, a 17th century retirement home for army veterans, and the river Thames, draws in over 150,000 visitors each year.

This year, with the London 2012 Olympics fast approaching and the nationwide celebrations for Queen Elizabeth's 60th anniversary as monarch two weeks away, the show had a definite patriotic feel to it.

Union Jack flags were ubiquitous, dotted around displays, woven into patterns in the flowerbeds and even adorning the jackets, t-shirts and dresses of attendees.

To commemorate the Queen's Diamond Jubilee, a number of growers unveiled new varieties of flowers. In rose grower David Austin's installation, the pale pink Royal Jubilee romped with the fiery Fighting Temeraire and white Tranquility varieties.

CHELSEA RED

Adding a nostalgic touch, the Chelsea Pensioners, the residents of the Royal Hospital, turned out in force in their unmistakable bright red overcoats to pose with members of the British Korean Veterans Association by a garden that recreated the landscape found in the demilitarized zone between North and South Korea.

The Great Pavilion, the central display tent, housed over 150 exhibits and thousands of flowers, where the heady scents of lilies, roses and other garden favorites vied with wafts of expensive perfume for supremacy.

Perhaps also reflecting the more sober economic backdrop, there were a greater number of visitors clutching cups of upmarket tea or coffee than the more usual champagne flutes.

The flower show attracts a varied audience, from green-thumbed television personalities, to business executives and social high-flyers, as well as the many celebrities that lend their faces to individual gardens.

Formula 1 boss Frank Williams posed with a topiary in the shape of one of his Williams team F1 cars, complete with topiary pit crew, while Britain's Got Talent judge Amanda Holden posed in a replica Corsican garden, complete with fragrant olive trees, lavender, rosemary and stone sheepfold.

Former Beatles' drummer Ringo Starr unveiled an artisan garden sponsored by WaterAid, a charity geared towards providing clean drinking water in developing nations.

"I truly believe everybody should have clean water and I'm just doing my small part to make sure that happens," Starr, a passionate environmentalist, said.

Towering above the show was the Westland Magical Garden, a multi-storey pyramid that featured level upon level of gardens designed by award-winning gardener Diarmuid Gavin, who set out to explore the idea of making the most of precious open space, especially in urban settings.

Comedy actor Ricky Gervais, the acid-tongued former Oscar host and star of the original TV comedy series "The Office", said he was in awe of what he called "true artists at work"

"It's fantastic that they try, particularly with the installations, where they have to bring out how beautiful it is naturally. It sends a chill down my spine," Gervais said.

Chelsea Flower Show, which is organized by the Royal Horticultural Society (www.rhs.org.uk) runs from May 22-26.

(Reporting by Amanda Cooper, editing by Paul Casciato)

• A Permanent Economic Emergency