Overtime is costing police millions of pounds a year – with some officers earning more than £20,000 on top of their salaries.

Cash-strapped Sussex Police has seen its overtime bill rise from £5.2m to £7.4m over the last three financial years.

Officers’ representatives say extra hours are part of the job, but anyone working too much could be putting their health at risk.

Overtime has been highlighted as a major issue for police paymasters this week, with the national bill rising from £9.8 billion in 1999 to £14.5 billion last year.

On average the 3,200 officers at Sussex Police took home an extra £2,318 in pay over the last financial year.

The force is aiming to slash its overtime budget by 8% this year.

Overtime is paid at “time and a third” if on officer is kept on duty at the end of their shift, time and a half if a rest day is cancelled at short notice or double time for a bank holiday.

Officers have to be authorised by a senior officer to work the extra time.

Bills for senior commanders can spiral if a major policing event takes place on a Bank Holiday, such as the Smash EDO demonstration in Brighton on May Day last year, which cost more than £500,000, or takes place at short notice, like the March For England event and counter-demonstration in Brighton on April 25, which was feared could cost more than £100,000.

Officers can also be called to give evidence in court at short notice on days they should be off work – which becomes more likely when shifts cover weekends with days off in the week.

The Centre for Crime and Justice Studies at King’s College, London, said although spending on overtime nationally has increased by more than 88% over the last decade, overtime pay per officer has remained roughly the same.

The rise is due to the increase in the number of officers in each force.

Bob Brown, who took over as chairman of Sussex Police Federation last month, said: “Our members would rather be able to do their duty within the time slots on their shift patterns and go home and have some quality family time.

“When you come on duty you don’t know what is going to happen in the next eight hours. If something happens just before the end of the shift, depending on the incident, if you are a witness or a major person in that investigation you have got to stay on.”

The sergeant with most overtime earned £20,800 last year; the constable with the most earned £16,552.

Sussex Police said they were both detectives involved in major investigations and their overtime far exceeded any other officers’.

Human resources director Marion Fanthorpe said: “We are a 24-hours-a-day, seven-days-a-week organisation serving the people of Sussex and we need the resources and flexibility to deal with any event or crime at any time.

"Overtime last year accounted for barely 5% of our pay budget and just 2% of our total budget.

"We also carefully monitor overtime trends to ensure cost effectiveness as part of our continuing effort to reduce costs wherever we can, and have already budgeted for a 8% decrease in overtime for this current financial year. However that must not be done at the cost of our service to the public."