A surgeon being investigated by the General Medical Council amid allegations about his treatment of more than 1,000 breast cancer patients is also facing a criminal inquiry, police have confirmed.
West Midlands Police said they were liaising with the Crown Prosecution Service to determine the course of the investigation into the conduct of Ian Paterson.
Mr Paterson is alleged by a law firm representing some of his former patients to have performed up to 1,150 "unnecessary, inappropriate or unregulated" operations while working at various NHS and private hospitals.
Thompsons Solicitors, which is pursuing negligence claims for several women, said Mr Paterson worked at a number of NHS and private hospitals from 1994, including those run by Heart of England NHS Foundation Trust, which covers hospitals in Sutton Coldfield, Solihull and Birmingham.
In a statement issued on behalf of Mr Paterson, the Medical Defence Union (MDU) said he was co-operating fully with the GMC investigation.
A spokeswoman for the MDU said: "He cannot comment further due to his duty of patient confidentiality and the ongoing investigation."
An investigation into Mr Paterson by the General Medical Council potentially spans up to 700 cases of an unregulated procedure that involved leaving some breast tissue behind after a mastectomy, Thompsons said.
It is further alleged that up to 450 women could have had invasive breast surgery when a biopsy might have been sufficient.
In a statement confirming the police inquiry into Mr Paterson, who has not been arrested, Detective Chief Inspector Matt Markham said: "West Midlands Police can confirm it has received a referral from the General Medical Council in relation to allegations about the medical practices of a surgeon who previously worked in Solihull.
"A criminal inquiry has been launched and the force is working closely with the Crown Prosecution Service to determine the course of the investigation."
Kashmir Uppal, a senior medical negligence solicitor at Thompsons, said she believed patients had been subjected to needless worry and risk.
She said the law firm was also liaising with the GMC, which regulates all doctors in the UK, to assist its investigations.
Ms Uppal added: "The women who have come forward so far have been very brave.
"Hopefully all who have had unnecessary or inappropriate treatment will seek reassurance or justice."
Mr Paterson's registration with the GMC was suspended following an Interim Orders Panel meeting on October 29.
A GMC spokesman said: "This means the doctor cannot work as we investigate concerns about his fitness to practise."
Thompsons is representing nearly 100 women, including Paula Gelsthorpe, from Nottingham, who had two lumpectomies when her condition was benign.
In a statement issued by her lawyers, she said: "I'm speaking out to make people aware.
"I was oblivious to what was going on until I received a letter saying there were some irregularities.
"When I was told my operations had been totally unnecessary, I couldn't believe it. I felt relieved at first, but now I feel angry and betrayed."