Mrs Regan, 53, was found dead at a flat on Marlborough Grange, Leeds, at 7pm on Sunday, West Yorkshire Police said.

Her 20-year-old grandson was arrested on suspicion of murder and is in police custody.

A post-mortem examination was due to take place to discover the cause of Mrs Regan's death but police sources said she had been stabbed.

It is believed her grandson, who suffers from mental health problems, was arrested earlier on Sunday in connection with an unrelated stabbing at Leeds railway station.

A 45-year-old member of railway staff was treated in hospital for a stab wound to his arm after the incident at 11.28am. He was stabbed with a knife after he challenged a man for trespassing at the station, British Transport Police said.

Following the news of her death, tributes to Mrs Regan poured in from across the country.

Mrs Regan began her campaign against guns and violent crime after her son, Danny, was shot dead in St Helens, Merseyside, in December 2002.

She founded her own organisation, Mothers Against Violence, in Leeds, and also had close links with campaign groups Mothers Against Guns and Mothers Against Murder and Aggression.

Dee Edwards, of Mothers Against Murder and Aggression, said: "She's made such a big difference to so many people's lives. This is an absolute tragedy for so many people."