The Union Jack, the ensign that sets British hearts fluttering and has for more recent generations of fashion designers and rock stars become a style icon, is now 400 years old.

The flag was introduced by King James I in 1606 when he melded together England and Scotland. Little did he know he was creating a fashion statement in red, white and blue. The first item that British designer Sir Paul Smith ever sold in his clothing store was a handkerchief bearing the Union Jack. Recently, when he was asked to do a version of Fritz Hansen's "Series 7" Butterfly Chair for its 50th anniversary, he emblazoned it with the flag.

The ensign became part of pop culture in the 1960s when Beatlemania and Carnaby Street made London swing. It's since been embraced by the Who, Oasis, the Spice Girls and Queen - the rock band as well as Elizabeth.

The Union Jack has also been used to good effect on the Mini Cooper, and footballer David Beckham sports one as part of the Reebok shoe brand.

The "Union Flag", to use its proper name, is a clever combination of England's cross of St George, Scotland's cross of St Andrew and Ireland's cross of St Patrick (though only Northern Ireland is part of the United Kingdom).

The Welsh dragon doesn't appear on the flag, incidentally, since, when the flag was conceived, Wales was not a separate principality but a part of England.

The flag can be seen flying above the queen's residences - Buckingham Palace and Windsor and Sandringham castles - when she's not there. Her presence is signified by the Royal Standard.

But while it's seen less in its official role, atop important buildings for example, than ever before, its popularity as a design icon has grown. Shoppers can find no end of products bearing the emblem, everything from ties and cufflinks to baseball caps and polo shirts.

Many British brands have incorporated the Union Jack in their designs, such as Dr Marten boots. Strangely, the Lonsdale shops, originally located just off Carnaby Street, has hidden the flag behind its name on products.