The boom in fast food outlets is fuelling a rat population explosion in Sussex, according to a national report.

But the number of mice in the county is falling.

The National Rodent Survey Report for 2001 found the number of brown rats across Sussex, Kent and Surrey had increased by 21 per cent in the past two years.

The survey, carried out by the National Pest Technicians Association (NPTA), also showed an 11 per cent increase in summer rats.

Across the UK, there was an 18 per cent increase in brown rats and a 31 per cent rise in summer rats.

The number of house mice in the South-East fell by one per cent, compared to a five per cent drop nationally.

The survey was carried out among all UK local authorities.

An NPTA spokesman gave a variety of reasons why the rise in fast food outlets had contributed to the rat population increase.

He said: "Many fast food outlets are continuing to create litter, with the public also tolerating poorer rubbish standards.

"The continuing use of black plastic bags without bins and the increase in fly-tipping of rubbish, including food waste, now many local authorities are not allowing free waste disposal at their civic amenity sites, are all reasons."

The report also blamed global warming for raising temperatures, so failing to kill off more rats' offspring.

Another reason was extensive bird feeding by residents in some areas.