Genetic mutations have produced a new breed of "super rat" with DNA that protects the vermin from standard toxins, according to Professor Robert Smith at the University of Huddersfield.
Ratcatchers in Berkshire and Hampshire were the first to report that their poisons were no longer effective, which experts put down to increased immunity among the pests.
But as the poison-resistant rats continue to spread, tests have revealed that they boast an entirely new strand of DNA that wards off attacks from pesticides.
Swindon in Wiltshire is the latest town to suffer an infestation, with exterminators reporting a 500 per cent increase in the rodents. Many are turning to traps, air rifles and even dogs in an effort to keep the populations under control.
Prof Smith of the university's applied sciences department warned that "super rats" may be thriving in communities across Britain. The Government no longer provides funding to track resistance, meaning the scale of the problem is unclear.
"Natural selection means that when you have a rat population in your town, poison will kill the ones that aren't resistant, the ones that survive may have the gene, they then have babies who can receive the gene themselves," he said.
"There are mutations and changes in their DNA that alter the ability of rats to deal with these poisons. It appears to be moving west and has now been located in Swindon and Bristol. It is a warning of things to come."
There are now thought to be around 80 million rats in Britain, a rise of more than 200 per cent since 2007.
The National Pest Technician Association has said that the scrapping of weekly bin collections in many councils has contributed to the explosion, with householders now keeping their rubbish bags outside for longer.
The British Pest Control Association (BPCA) is calling go the Government to approve more powerful pesticides for use outdoors, warning of a threat to public health if rat numbers swell over the summer.