So vein: Tara Palmer-Tompkinson shows off her ultra-muscular arms

Instead, something else muscled in on the act.

Tara Palmer-Tomkinson's biceps, threaded with bulging veins, got all the attention.

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Beauty and the bicep: Tara Palmer-Tomkinson shows off her sinewy arms in her strapless gown

Her sinewy arms led to unflattering comparisons with Madonna, who showed off a similarly sculpted look in a revealing vest top last year.

Miss Palmer-Tomkinson, 36, had dressed up to attend an exhibition at the National Portrait Gallery in London.

Her dress did at least show off her enviably slim figure.

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Fat free: The ultra thin socialite appears to be taking style cues from Madonna as she revealed her bulging, veiny arms

But as a former cocaine addict who has struggled to keep the pounds from melting away, she has always been sensitive about her shape.

At the height of her drug problem, her weight dropped to a mere six stone.

In the past, she has denied that her tiny size zero frame (a British size four) is a reflection of her health.

"I have this very muscly, skinny body and I don't like it," she has lamented in the past.

"I tell my friends I'm on the doughnut diet but I can't put the weight back on. If I went to the gym, I'd bulk up. I hate my muscles. They're all veiny.

"I always put my arms up in the air before I get out of a car so the veins don't stick out. I'm strong, though. I'm always the one who can get the lid off the jam jar."

Prominent veins are often attributed to overtraining and excessive weight-bearing exercises.

Veins become visible as body fat is stripped away, indicating a lack of nutrition. Harley Street surgeon Apostolos Gaitanis said: "She may be genetically prone to having large veins, but this appears to be due to over-training. There is no fat to disguise them."

At least Miss Palmer-Tomkinson is not alone.

As well as Madonna, Angelina Jolie is a member of the veiny arms club.

She displayed painfully thin arms with prominent veins last year.

The 32-year-old actress, already remarkably slim, claimed she had lost weight suddenly in the aftermath of her mother's death.

At the same time she was breastfeeding her baby and looking after her other children, which exacerbated the weight loss.