MUTANT super-rats which are immune to some poisons are roaming Oxford, according to a rodent expert.

Prof Rob Smith made the claim after extracting DNA from the tail of a rat found dead in Oxford and conducting molecular tests.

He said that he had found the same resistant gene mutation he previously found in the resilient rats in Hampshire.

The rodents have been labelled super-rats by Prof Smith, Dean of Applied Sciences at Huddersfield University.

The rats are stronger thanks to an ability to resist the usual kind of poisons laid out to kill off the pests.

Oxford City Council has insisted its poison is working and has asked to see Prof Smith's report.

But Dr Frances Kennett, of Jericho, who has campaigned against fortnightly waste collection, said the emergence of the so-called super rats meant the city council should immediately return to weekly waste collections.

Prof Smith said: "This form of rat has been found in the past across the South East, in the countryside in Berkshire, Hampshire and parts of Oxfordshire, but this is the first time the super rat has been found in Oxford city.

"There are still some poisons that can be used against super rats, but they are so toxic that they cannot be used outdoors.

"The environmental health department dealing with outbreaks of rats will find that if certain types of poisons are no longer effective they will have to use traps.

"We know from a study based in Oxford that rats can carry up to 14 diseases including salmonella and Weil's disease, which can prove fatal."

Prof Smith said the super rat test was conducted after Oxford residents linked rat sightings to the switch to fortnightly waste collections.

He said: "The Department for Environment, Food and Rural Affairs, used to monitor the spread of rats' resistance to poison, but stopped 12 years ago and the Department of Health does not seem to have any interest in rats either.

"These resistant rats eat poison and are not affected by it so they become parcels of poison running around."

Dr Frances Kennett, 62, last year withheld her council tax after claiming her home was overrun by rats following the switch to fortnightly collection.

She said: "I am appalled that these rats are apparently no longer responding to certain poisons and I feel this justifies my point about the need to return to weekly waste collections. My drains have been relined at a cost of £1,400, but it has not made any difference - I am still getting rats."

Jean Fooks, executive member for a cleaner city, said: "Our environmental health team tell us there is no evidence that their standard poisons are not working and they would like to see a detailed report from Prof Smith.

"The suggestion that Oxford is being over-run by super rats is just not right - something killed the rat in the first place that was used for these tests.

"The switch to fortnightly collections has not led to an increase in the number of rats in Oxford."