Fiona Shackleton is Britain’s most famous divorce lawyer. She represented Sir Paul McCartney when he divorced Heather Mills, a case that saw Mills’ achieve some further infamy when she poured water over Shackleton’s head.

Now, Fiona Shackleton, who as a Conservative Party peer is properly entitled “Baroness Shackleton of Belgravia”, is being sued by a sociate client who is deeply upset over the size of the law firm’s bills which, says client Mortimer Whealon, are “ridiculous” and account “for every second of their time, even if you haven’t asked for it.”

The Telegraph reports Whealon saying, “If they are calling you on the phone, or even so much as thinking about your case, the next thing you know you are receiving bills for £600 an hour, which is just crazy.”

She adds: “Divorce is stressful enough, and so to take on your own divorce firm, well, you can only imagine.” Four of the firm’s bills are now being assessed by the court.

The court has already ruled in the firm’s favour on seven other bills. A spokesman for Payne Hicks Beach said at the time that all the clients had confirmed that they were happy with their bills.A spokesman for the firm says Whealon was never one of the peer’s clients.

Of her claims, that its hourly rate “was agreed in advance”, he says: “She is wrong that the bills were calculated on the basis of £600 per hour.”