Three leading pathologists have accused the Metropolitan Police of attempting to discredit them as expert witnesses in so-called Shaken Baby court cases.

About 250 Non-Accidental Head Injury (NAHI) cases go to court every year, with the outcome often relying on a expert testimony from pathologists.

The Royal College of Pathologists has called for an inquiry into the claims.

Responding to the allegations, the Met said the force was "completely committed to the judicial process".

The scientific debate over NAHI has grown increasingly acrimonious over the past 10 years.

At first it was played out in select gatherings of pathologists before ending up in courtrooms and inquests up and down the country.

That debate turned toxic, with one side accusing the other of proselytising suspect scientific theories.

Now, senior consultant pathologists have accused the Metropolitan Police and others of an orchestrated strategy to discredit them as expert witnesses for parents and carers accused of murdering their children.

Dr Waney Squier, Dr Irene Scheimberg and Dr Marta Cohen say their evidence is based on a speech made by Detective Inspector Colin Welsh, a lead investigator with the Met's Child Abuse Investigation Command.

The BBC has obtained a version of the speech made at the 11th International Shaken Baby conference in Atlanta, September 2010.

In this speech, DI Welsh referred to a meeting in 2008 attended by representatives of the police, medical experts and CPS officials at which the "impact and effect of contradictory expert evidence" was discussed. The Met has confirmed the meeting took place but said it was standard procedure following an acquittal in a court case.

According to a note by a Seattle-based lawyer called Heather Kirkwood, DI Welsh talked about the failure of a number of high profile Shaken Baby prosecutions and stated the number one problem as "defence expert testimony".

He suggested as tactics to question everything about them - qualifications, employment history, testimony research papers presented by these experts, and even going to their expert bodies "to see if we turn up anything".

DI Welsh is also reported to have referred to "judicial inexperience", using the term "so deal with back door" apparently in reference to relaying concern to judges about expert witnesses.

A police spokesman confirmed that DI Welsh had given the speech but added that The Metropolitan Police Service "is completely committed to the judicial process and would never seek to improperly influence it".

Complaints

The pathologists, however, say they were all the subject of inquiries by outside bodies initiated by the Metropolitan Police and others.

Dr Squier, who works at the John Radcliffe Hospital in Oxford, was the subject of two separate inquiries last year.

The Human Tissue Authority investigated a complaint that Dr Squier may have retained human tissue, a criminal act if true. The accusation was found to be without foundation.

The complainant was identified as an officer with the Met.

DI Welsh appeared as an "interested party" in a second inquiry by the General Medical Council into Dr Squier and Dr Cohen.

The GMC inquiries resulted in both doctors being brought before emergency Interim Orders Panels, but proved inconclusive.

The Human Tissue Authority also conducted an inquiry into Dr Scheimberg following a complaint from a colleague based at Great Ormond Street Hospital. She was also cleared.

Professor Tony Risdon often acts for prosecution teams and made his complaint about Dr Scheimberg based on information from a third party but which he personally could not verify. He declined to comment when approached by the BBC.

Investigation call

Dr Squier defends the evidence she gives, saying a court "should be able to hear evidence for both prosecution and for a defence and that anybody who has a valid and sincere opinion should be given the opportunity to express that opinion in court".

"And it appears to me that there has been an attempt to remove from the courts all of those people who are willing to challenge the mainstream hypothesis, even if those opinions are sincerely held and are based on a lot of day-to-day experience and are based on a thorough grounding in the current evidence available in the scientific literature."

A spokesman said the Metropolitan Police Service had registered concerns "about certain practices of a doctor in December 2009" but declined to comment on the reasons.

"We are aware of a report registered by the National Policing Improvement Agency with the General Medical Council regarding two doctors. The MPS has co-operated with a request from the GMC in June 2010 to provide any relevant information," the spokesman added.

Professor Peter Furness, President of the Royal College of Pathologists, expressed concern about the allegations of a campaign.

"The allegations that there has been a systematic attempt to intimidate people from presenting their honestly held views to a court should be investigated," he says.

"I would normally suggest that should be investigated by the police, in this case at least some of the allegations it appears the police have been involved in it.

"There are processes for conducting investigations into police activity. It sounds to me from what I've been told that those mechanisms should probably be used.

"My concerns about this are as a private citizen not as president of the Royal College of Pathologists. I think anybody who feels the process of justice is being illegitimately subverted ought to feel concerned and ought to try to do something about it."

The BBC approached a significant number of pathologists who act for prosecution teams. They all declined a request for an interview, some saying they too had been the subject of threats and complaints.