Health bosses say more than 20 patients are being seen by a special GP service because they have attacked or threatened their own doctors.

NHS Leicester City and NHS Leicestershire County and Rutland primary care trusts have released details of the number of dangerous patients as it emerged there has been a rise in the number of assaults on GPs and their staff.

The trusts pay for a special service provided by a surgery, in Narborough, for patients who have been refused treatment by their own doctor because of their behaviour.

Toby Sanders, director of primary care for the PCTs, said: "Violent and threatening behaviour towards staff at GP practices is unacceptable."

Between April 2010 and March this year, 15 city patients and eight county patients were seen at the Narborough surgery under the trusts' zero tolerance to violence scheme.

The previous year, April 2009 to March 2010, 23 city patients and seven from the county were seen.

Despite the zero tolerance policy towards violence, GPs say striking patients off their registers is only ever a last resort.

Dr Mohamed Roshan, who runs The Willows Medical Centre, in Evington, said: "GPs are quite vulnerable – you aren't protected in any way and if you suddenly find you are being threatened with physical violence it comes as a surprise.

"The last time it happened to me was in about 2007, when a patient threatened to get violent.

"It was a shock and can be quite frightening, especially if the patient is physically bigger, and we can't really retaliate."

Dr Roshan said he was once threatened by patient with a weapon.

He said: "That was in about 1990 when a patient suddenly drew a knife, but I wasn't hurt. However, our receptionists do put up with a lot of verbal abuse from patients."

Mukta Modi, practice manager of the Northern Heights practice, in Northfields, and the Canon Street practice, in Belgrave, said: "It is not a big problem."

In 2010, police were called to 14 incidents in Leicestershire's surgeries – twice the number reported in 2007. Last year, six doctors were assaulted with three receptionists, three nurses and two patients also attacked.

Police figures show out of 38 incidents in the past four years in Leicestershire, only one, in January 2007, involved a weapon which was a knife.

A Leicestershire Constabulary spokesman said: "No-one, regardless of their occupation deserves to be the victim of an assault."