When funds are stolen from the NHS, it means less money to treat sick people.

The health service may not seem like an obvious victim of fraud but because of its size, the opportunities are vast.

It could involve staff, patients or outside companies in huge variety of ways.

Amounts of money involved can also be massive – during the year 2007-2008, investigations by the NHS Counter Fraud Service saved £7.5m nationally. Since it was set up in 1999, the service has recovered more than £57m.

Across the country there are more than 300 Local Counter Fraud Specialists who work in NHS organisations to prevent fraud, investigate allegations and prepare cases.

Though their number is relatively small, their remit – and their importance – is massive.

As the largest hospitals trust in the UK, Leeds Teaching Hospitals has an annual budget of nearly £900m and more than 14,000 staff.

Ensuring that money is used for looking after patients and running the hospitals is the responsibility of local counter fraud manager David Gregory and his team.

Together with local counter fraud specialists Richard Schmidt and Lina Anderson, they work to combat all forms of fraud involving the hospitals trust.

The team's most common cases involve sick notes, such as them being forged, altered or employees working elsewhere whilst off sick.

Timesheet fraud, or claiming for overtime not worked, as well as fraudulent expenses claims are also frequently seen.

The team's role is to investigate activities like these – but also to prevent people from having the desire or the chance to commit fraud in the first place.

"We are trying to create an anti-fraud culture, promote the work we are doing and deter people from fraud," Mr Schmidt said.

"What we are trying to do is deter people, say 'think again, there's somebody watching you'.

"We want to reduce the risk of fraud in systems. If the right controls are in place, people should not be able to do it."

That means their prevention work is just as important as investigating cases of suspected fraud.

June is national NHS Fraud Awareness Month which aims to show the effects of fraud and how it can be stopped.

In order to developing better systems to prevent fraud, they will review the ways of running wards or departments.

"We identify one or two areas each year where we look at their policies and procedures and see how these work," Mr Schmidt said.

Because of their potential for misuse, one of the things they've cracked down on is sick notes.

They discovered an employee who had taken a block of sick notes and was issuing them to herself.