An ambulance driver caught by a speed camera doing 104mph while delivering a liver for transplant escaped prosecution yesterday when charges against him were dropped.

Mike Ferguson, 56, attracted public sympathy when police charged him with speeding on the A1 in Lincolnshire. He was delivering the organ from St James's Hospital in Leeds to Addenbrooke's Hospital in Cambridge last January.

He had been due to appear at Grantham magistrates' court on Monday. But the Crown Prosecution Service dropped the charge, saying a prosecution "was not in the public interest".

Mr Ferguson, of Birkenshaw, near Bradford, said: "The fight does not stop here. I am going to continue campaigning to clarify the law so that other emergency service drivers don't have to suffer the same experience." Mr Ferguson said organs had to be delivered as fast as possible. He was backed by his union, the GMB, and a 20,000-signature petition was handed in to Downing Street this week.

John Durkin, the union's branch secretary for ambulance drivers, said: "If Mike had been found guilty, the repercussions throughout the service would have been very damaging."

But Ken Williams, a trustee of the RoadPeace campaign, the charity for road crash victims, warned of the danger posed by emergency vehicles travelling at high speed.