A British heiress has started divorce proceedings in the wake of claims that Lindsay Lohan had sex with her musician husband in the toilet of a rehab clinic.

Sensational divorce papers identifying Mean Girls star Lohan were filed last week by US lawyers acting for Stephanie Allen, 28, whose family is worth $720 million.

Mother-of-two Stephanie, from Lincolnshire, pulls no punches against her husband Tony, 39, the Dead Stays Alive frontman, in the 52-pages filed in Chatham County Court in Savannah, Georgia.

Stephanie states that her three-year marriage “is irretrievably broken” and gives the grounds for divorce as his “adultery” and ‘cruel treatment.’ The papers also accuse her husband of being “guilty of habitual drug addiction” and that she should retain custody of their eight-month-old twins.

The lawyers do not name Lohan in the actual complaint but they refer to her husband’s “conduct and relationship with another woman” as described in an American magazine and on showbiz internet sites.

But Exhibit ‘A’, which is attached to the divorce papers, includes articles claiming Lohan, 21, who has had an on-off affair with Calum Best, started a relationship with Tony Allen while they were both being treated at the Cirque Lodge clinic in Utah.

One of the articles attached to the exhibit was featured last week in America’s In Touch magazine. It states that there has been “no word on whether or not Tony was the fellow rehabber caught bonking Blohan in a Cirque Lodge john.”

Stephanie’s lawyers chose the magazine article to support her case for divorce because it quotes an onlooker as saying: “They looked very cute together. You could definitely tell from watching them that there was something going on. It was very apparent they were a couple.”

Another insider reportedly told the magazine: “He’s an artist, so he and Lindsay could relate. No-one else in rehab at the time was in the entertainment industry, so I think that’s how they started talking, and they bonded that way.

“They were bound to get close