The number of people convicted of violent attacks against NHS staff has risen 15-fold in two years, according to figures published yesterday.

There were 759 successful prosecutions in England in 2004/2005 from a figure of only 51 in 2002/2003. The rise was welcomed by the health secretary, Patricia Hewitt, and public sector unions, but they said it also highlighted the extent of the problem.

Mrs Hewitt said: "Violence against NHS staff is completely unacceptable ... The huge increase in prosecutions demonstrates that we will take tough action against anyone who attacks them."

A drive begun in 2003 to tackle the problem of patients assaulting health service workers is being credited with the increase in convictions.

The NHS Security Management Service operates a national reporting scheme for tracking repeat offenders. It is also set to sign an agreement with the Association of Chief Police Officers that will commit both organisations to working more closely in investigating cases and prosecuting offenders.

Keith Nicholles, a paramedic from the North East Ambulance Service, was punched by a patient, who was sentenced to six months for the assault. Mr Nicholles welcomed the rise in convictions.

"In the past we've been a soft touch. This will give us a bit of clout," he said.

Karen Jennings, head of health at Unison, said: "It's good to see that we are now taking violence against NHS staff more seriously, but it's shocking that ... NHS staff are suffering from violence on a daily basis."

Unison wants a law that makes assaulting a public sector worker a specific offence.