The Queen has been branded a frock horror by an American dress designer in his annual guide to the "dull, dowdy and devastatingly dreary".

She came in third on Mr Blackwell's 40th annual worst-dressed women list.

She was pipped at the post by the actress and singer Cher - famed for her outrageous flesh-revealing outfits - and Canadian chanteuse Celine Dion.

Mr Blackwell, a former fashion designer known only by his surname, deemed the Queen's choice of a harlequin-style dress at December's Royal Variety Performance in Birmingham a disaster.

"Was she the palace Christmas tree or just a royal clown?" asked the Los Angeles-based columnist.

Mr Blackwell, who writes for a US tabloid, was not the first to comment on the Queen's vivid multi-coloured sequinned outfit.

Australian "housewife superstar" Dame Edna Everage - aka Barry Humphries - declared herself delighted that Her Majesty was following her flamboyant fashion sense.

Some commentators compared the outfit to that of a court jester, others that it was simply "too loud".

But the rainbow dress was not enough to merit first place on the list. That honour went to Cher, whose unique style was recently described as an inspiration to drag queens everywhere by a UK entertainment magazine.

Mr Blackwell described her look as "a million beads and one overexposed derriere".

Celine Dion - best known for her Titanic song My Heart Will Go On - came in second place. While the multi-platinum singer has little trouble hitting the high notes, her fashion sense was dubbed decidedly off-key.

"In her backward tuxedo there's no way of knowing whether Diva Dion is coming or going - a profusion of confusion," declared Mr Blackwell.

Navel-flaunting teen sensation Britney Spears fared little better coming in at number six:

"This belly-baring songbird is better heard than seen."

Actress and pin-up Cameron Diaz was also criticised for her "freaky" fashion sense.

Mr Blackwell also branded Friend's star Jennifer Aniston a "fashion bore and a snore" - although she has regularly topped the best-dressed lists in fashion magazines worldwide.

But the columnist did find something complimentary to say - declaring that Gwyneth Paltrow, Sophia Loren, Oprah Winfrey, Camryn Manhein, Barbra Streisand, Halle Berry, Helen Mirren, Nicole Kidman, Sharon Stone and Princess Caroline of Monaco were "fabulous fashion independents".