The Cat Protection League said the risk of a plague of cats, fuelled mainly by unwanted and abandoned kittens, was now so great that it had launched a nationwide neutering campaign to prevent the problem becoming an "epidemic".
Of the estimated 7.5m cats in the UK, a spokesman for the charity said there were at least one million who had not been neutered and that figure could multiply to more than seven million by the year 2010.
One single female cat, over five years old, can be directly responsible for as many as 20,000 descendants, he said.
"Despite their popularity, tens of thousands of unwanted kittens are being born each year only to be thrown onto the streets condemned to a life of starvation and disease," he added.
Mike McCawley, chief executive, said: "The public, especially so-called cat lovers, need further education to understand that by not neutering their cat, they are destroying its quality of life.
"It's truly amazing that people will allow their cats to reproduce constantly.
"Unneutered cats are also far more vulnerable to contagious and fatal diseases which spread more rapidly among those that have not been operated on.," he added.
"Not to neuter is sheer cruelty."
The warning came as a survey revealed that more stray dogs than ever before are being taken in by local authorities.
In a MORI survey commissioned by the country's largest welfare dog charity, the National Canine Defence League, it was discovered that 106,000 stray dogs were rounded up between April 1 1996 and March 31 1997 - an increase of 13 per cent.
One in six of the UK's strays, about 17,000 dogs, were destroyed. It is estimated that the problem costs the taxpayer pounds 11.5m a year.
However, of the animals that were not destroyed, half were returned to their owners and one in 10 were found new homes.
The survey also revealed that there is one stray dog for every every 100 people in Northern Ireland but only one per 2,000 in London.
Clarissa Baldwin, chief executive of the NCDL, said: "Education is the key to solving this problem. If people had their dogs neutered there would be fewer unwanted puppies and ultimately, fewer strays on the streets.
"If all dogs wore identity discs, as required by law, even more strays could be easily returned to their owners."Reuse content