Incidents at the QEH have risen from 46 in 2006-07, to 92 in 2010-11. The latest figures were revealed in a national report, which showed attacks on NHS staff increased slightly across the country last year.

Hospital bosses said the total had increased because more workers were coming forward to report attacks.

Staff at the QEH say 88 of the 92 'assaults' were carried out by people deemed not to have 'capacity' – for example, patients with dementia or similar conditions, who may not have understood what they were doing at the time.

Only four assaults occurred where the assailant was fully aware what they were doing, although staff declined to pursue a prosecution in each case.

Gary Morris, the hospital's security manager, said: 'The increase in reported incidents on the previous year is mainly due to improved understanding and reporting by staff.

'We have seen a steady increase over recent years in the number of reported assaults. This is because staff are now more willing to report incidents of physical or verbal abuse as they have seen action taken both by the trust and police.'

Gwyneth Wilson, the hospital's director of nursing, said: 'We adopt a caring approach to patients, particularly those who are here to be treated for a medical condition but who may also have dementia.

'Being in hospital can be very confusing for them and they may strike or scratch staff in their frustration, without realising what they are doing.'

Assaults fell at the James Paget Hospital, in Gorleston, where there were 46 attacks on staff in 2010/11, compared to 74 the previous year.

There were 145 assaults on staff at the Norfolk and Norwich University Hospital, no figures for last year were available last night.

Nationally, there were 57,830 assaults on staff in England in 2010/11, compared with 56,718 the previous year.

Of these, 69pc involved medical factors such as patients suffering mental health issues, learning difficulties or conditions such as dementia, up on the 61pc a year earlier.

The data, from NHS Protect, noted that assaults resulted in 1,397 criminal sanctions, up on the 1,128 in 2009/10.

Richard Hampton, local support and development services manager at NHS Protect, said he believed the increase in assaults was down to an improved culture of reporting assaults and better recording mechanisms.

Christina McAnea, Unison head of health, said: 'The increase in violence against nurses, paramedics and other NHS staff in England is a national disgrace.'