Swiss insurer Winterthur could be forced to drop its legal action against 600 solicitors who, it alleges, improperly fed personal injury claims to The Accident Group (TAG).

Winterthur is leading the legal battle against the solicitors who, it alleges, acted on behalf of claimants with dubious personal injury claims.

But in order to prove the solicitors negligence, the insurer must first gain access to the clients' files.

"Winterthur has to prove negligence in the TAG scheme," one legal expenses source said. "The problem is all the evidence is in the solicitors' files.

"Winterthur has to get hold of the files, and it is down to the judge to decide whether they [the solicitors] should hand them over."

A leading legal expert also cast doubt over whether the insurer could bring a class action such as this.

"If they are to prove negligence it would have to be done case by case, and not generically," the legal source said. "There is some doubt as to whether the judge will order the solicitors to hand over the files."

If the insurer was denied access to the files, Winter-thur's case "could collapse", he added.