Emergency services are to join forces to press for changes in speeding law exemptions after charges against an ambulance driver were dropped yesterday at the eleventh hour.

Mike Ferguson, who was clocked twice at an alleged 104mph on a late-night dash to deliver a donor liver for a transplant, said he was "ecstatic" at the decision.

Lincolnshire police, whose cameras caught Mr Ferguson on the A1 near Grantham in January driving a marked car with flashing lights, supported the calls for legal changes. As the law stands, an ambulance speeding to an accident is also vulnerable to prosecution.

Assistant Chief Constable Peter Davies said: "There is no exemption in law which permits any vehicle delivering blood or organs to be driven beyond the prevailing speed limit. I hope that the issues raised by this case will lead to the law being reviewed."

Mr Ferguson's union, the GMB, handed a petition with 20,000 signatures to the prime minister's office this week, calling for a change to the "absurd" regulations. A union representative, John Durkin, said: "If Mike had been found guilty, the repercussions would have been very damaging. We are all trained to drive safely at high speed. A few minutes make a big difference."

Mr Ferguson's local MP, Mike Wood, said he was hopeful "common sense" revisions would be made: "I have agreed to work with Lincolnshire police among others to see what changes need making."