A veteran member of Britain's ruling Labour Party announced she was leaving it today because she felt betrayed by its leadership under Prime Minister Gordon Brown and shocked by the behaviour of his team.

Alice Mahon, 71, a well-known left winger and former Labour member of parliament who often criticised former leader Tony Blair and opposed the Iraq war, said she was "scandalised" by a series of offensive emails sent by one of Brown's advisers.

"I've reached the end of the road with the Labour Party," Mahon told Sky television. "I've lost faith in the government and the direction they are taking us in."

One of Brown's most influential aides, Damian McBride, was forced to resign a week ago after sending emails containing unfounded smears about opposition Conservative leader David Cameron and his finance spokesman George Osborne to a Labour Internet campaigner.

The emails were leaked, and Brown was forced to apologise for his adviser. He said on Thursday he had been "horrified" when he found out what McBride had done.

Mahon said the scandal had shown her the kind of people who were running Labour.

"I think that most decent people in the party would be shocked and absolutely scandalised by the smears that were about to be launched on our behalf," she said.

"I cannot imagine what kind of person would think it is a good idea to smear a couple who have just lost a loving son," she said. The Camerons' six-year-old son Ivan died in February.

Mahon, who served as a Labour member of parliament for northern English Halifax constituency between 1987 and 2005, said she had joined Labour as a teenager, but no longer felt there was a place for people like her in the party.