There is a new generation of rats that carry a genetic mutation which makes them resistant to conventional poison.

A report from the University of Reading commissioned by the Campaign for Responsible Rodenticide Use (CRRU), has identified "the massive extent of L120Q resistance across the whole of central southern England."

The report highlights the situation in the region but makes it clear that the data is not available for the rest of the UK.

Dee Ward-Thompson, British Pest Control Association (BPCA) technical manager, said: “The study highlights the fact that resistance is growing in rat species across a swathe of the country.

“It also reports that rats without the genetic mutation are being killed off by poison, so the resistant species are taking their place, leaving a growing population of resistant pure-breds.

“With their numbers expanding there could be a significant risk to public health if their population is left unchecked, in both urban and rural environments.”

The study reveals that L120Q is the most severe form of rodenticide resistance identified to date.

Ms Ward-Thompson added: “The rise in resistance could be due to a number of factors. However, it is most likely the spread has been accelerated by the application of rodenticides, by amateurs such as home and business owners doing it themselves, or employing an unqualified individual to try to resolve the problem.

“The clear message is that, to be effective in tackling this issue, people should not attempt to self-treat rats.

“Professional use only rodenticides are often more successful, but most are subject to strict legislation, so it has become more important than ever before to make sure infestations are treated by experts.

“Rats must be dealt with by those with the skills required to understand rodent behaviour and their habitat, and who know how to treat any particular strain.

“By employing a member company through the BPCA referral service, the public can be sure they’re using a qualified technician who is able to purchase and apply relevant products that can tackle such issues of resistance.

“We’ve established strict criteria to ensure the professionalism of our members so companies carrying our logo will carry out safe, effective and legal treatments.”