'I know how Kelly felt,' says Caplin as the doors of No 10 close in her face

The increasingly strained relationship between Carole Caplin and Tony and Cherie Blair underwent a bizarre twist yesterday when the controversial "lifestyle adviser" suggested she might be under surveillance, possibly by security agencies linked to the Government.

Ms Caplin is also said to have claimed she has been the victim of an attempt to obtain details of her bank accounts, while her suppliers, who helped to dress Mrs Blair, have been interrogated and her movements monitored during a recent trip to the Maldives.

She told The Mail on Sunday, for whom she is employed as a columnist, that she was worried her telephone was being bugged and she was being watched, saying: "I understand how that man Kelly felt."

Another report yesterday, quoting sources close to Ms Caplin, said she was considering writing a book on her relationship with the Blairs, which has explosive potential. However, such a plan could be made difficult by the confidentiality agreement she has signed. The Blairs have rigorously enforced such arrangements in the past.

While Downing Street will not be happy about the suggestion of a book or her claims - particularly in the middle of the Hutton inquiry - of dark forces at work,it was saying nothing yesterday.

Ms Caplin, 41, a former model and dancer, has been advising Mrs Blair for almost a decade, and was reported to be receiving about £1,000 a week for her help. Last year she was at the centre of the "Cheriegate" row when her boyfriend, the convicted conman Peter Foster, became involved in helping the Blairs to buy two flats in Bristol.

Her continued presence in the Blairs' circle, and Mrs Blair's reluctance to have anything said against her, are known to have been a factor in the resignations of both Alastair Campbell and his partner, Fiona Millar, who was Mrs Blair's assistant.

However, signs emerged over the weekend that the Blairs - or those acting on their behalf - are attempting to distance themselves from a woman with the potential to cause trouble with her knowledge of life behind the doors at No 10. But it is unclear whether Ms Caplin's claims are a reaction to that.

During the "Cheriegate affair", Ms Caplin was questioned closely by Downing Street staff, she said yesterday. She claimed the questioning, about her suppliers and the discounts she obtained, was "so accusatory" that her lawyer was asked to be present.

In April, as part of a security review, Ms Caplin's swipecard pass to 10 Downing Street was withdrawn, which meant she had to pass through security screening with all other visitors. Whitehall sources said there was some "shock" that she had a pass in the first place.

One report yesterday said that in July, as the Kelly affair blew up, the Blairs agreed to keep Ms Caplin away from Downing Street, in a general desire "to get rid of anything which could be perceived as detrimental". Ms Caplin confirmed that she no longer visits No 10 and only sees Mrs Blair twice weekly at the gym, although she suggested this was her decision, not her client's.

But then the picture becomes murky. The Mail on Sunday says that in August, while Ms Caplin was in the Maldives researching a book on luxury spas, the suppliers of Mrs Blair's clothes were contacted by people claiming either to be a journalist or working for Downing Street, asking about clothes, prices and discounts. At the same time, a failed attempt was made to gain access to her bank accounts by someone with knowledge of her security codes.

In the Maldives, she claims, paparazzi appeared to have prior notice of her movements. "I'm terrified, and I don't know why they're watching me like this,'' she said.

Since "Cheriegate" there have been several incidents to make Mr Blair, if not his wife, wary of Ms Caplin. First, there was the BBC crew allowed into her flat at the height of the affair, followed by the interview she gave to Hello! on her failed relationship with Foster, her miscarriage and "the truth about her friendship with the Blairs".

Then, in August, came the publication in Marie Claire of a photograph of Ms Caplin applying lipstick to Mrs Blair while sitting on the prime ministerial bed.

Although Ms Caplin says she had no part in arranging the photo-shoot, and points out that the picture shows her trying to stop the photographer, it gave rise to renewed pressure for her removal. In a further twist, The Mail on Sunday claimed the photo-shoot was set up by Ms Millar, who failed to supervise the photographer.

Ms Caplin's interrogator over her suppliers was Hilary Coffman - a Downing Street aide and the wife of David Hill, Alastair Campbell's successor - who is said to be unhappy at Ms Caplin's influence. Whether Ms Caplin will survive the "post-spin" era at Downing Street to claim victory over Ms Coffman and Mr Hill - as she is said to have done over Ms Millar and Mr Campbell - remains to be seen.