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She claims she has dropped two dress sizes after splitting from her boyfriend Seb Chew.

But sources say the real reason behind Lily Allen's recent weight loss: she is paranoid over her "chunky" thighs, ankles and rear and has been mortified by magazine articles picking up on her larger lower half.

Her new management team have sent her to "Body Doctor" David Marshall in Primrose Hill, who has been giving her intensive diet and training sessions to help her tone her legs.

The fitness guru, who is famous for bringing model Sophie Dahl from a size 18 to a 12, has put Lily on his six-week one-on-one course.

And the results are not just showing on her lower half - the 22-year-old is also noticibly thinner in the arms and face.

The singer has cut out sugar and wheat, and is on a diet of fish, lean meats and steamed vegetables.

On top of this, she has to drink a special juice of ginger, beetroot, carrot, apple and celery, as well as concentrated artichoke and celery juice tonics three times a day.

Marshall - who can also boast Ant and Dec, Frank Lampard and Rio Ferdinand among his clients - is not known for mincing his words, and his training sessions with feisty Lily often turn the air blue.

A source says: "He pushes people very, very hard. He'll shout at her, 'Come on Lily, one more', and Lily will scream back 'F**k off you b*****d!'

"She is very conscious about how her figure is portrayed in the media, and is paranoid about her chunky bottom half.

"It was her new management team that recommended David, and they were keen for her to get back into shape. She has been working out every other day, with particularly gruelling exercises to get rid of her 'cankles' ? where her calves join her ankles.

"David makes her do controlled weight training, doing 25 reps with a heavy weight. It's pretty agonising, but Lily keeps coming back for more. She is four weeks into her six-week course, and has already dropped two dress sizes."