Swarms of wasps are plaguing Oxfordshire householders, with pest control experts struggling to cope with the highest numbers for years.

Guy Watkinson, of Rentokil, tackles a wasp nest at the Bowyer Arms pub, in Radley

People are being warned of the dangers of potentially lethal wasp stings following what one council described as "a dramatic increase" in nests.

The Witney branch of Rentokil said there had not been so many wasps since 1997. Calls from householders and businesses wanting nests destroyed are up 20 per cent on last year.

Branch manager Derek Bird said there were many more calls from people asking for advice.

His 18 technicians were having to work overtime and the branch was considering employing extra staff.

Mr Bird said: "There has been a significant increase in the number of wasp nests this year. We have had our work cut out."

Dr George McGavin, assistant curator of entomology at Oxford University Museum of Natural History, said the increase in worker wasps was the result of more queens surviving the relatively mild winter.

He said: "The worker wasps will die off by September or October, so they're nearing the end of the season and are desperately searching for food.

"They're seen as complete pests, but they're actually wonderful. They're brilliant for gardens."

Oxford City Council did not have any information available about the city's wasp population. But Helen Bishop, a spokesman for the Vale of White Horse District Council, said its pest controllers were receiving about 40 calls per day about wasp nests.

It has also taken on extra pest control contractors.

She said: "Last year, the number of wasps was quite low, so there has been a dramatic increase. This is about the number of calls we expect during a high period."

Pest controller John Richens, 52, of Bletchingdon, near Kidlington, usually works alone, but has employed another member of staff because the demand has increased so much because of wasp numbers.

He said: "I wouldn't quite say there's an epidemic, but there are a lot more wasps around than usual. Luckily, we don't have any species which cause really nasty stings, but it can be dangerous if they swarm."

Paul Montgomery, training manager for St John Ambulance in Oxfordshire, said: "A sting on the mouth or in the throat is potentially dangerous. People can also go into shock, which is a massive allergic reaction.

"The person will need emergency treatment, which will involve an injection of epinephrine (adrenalin). If in doubt, get an ambulance out."