47.2 per cent of households with a cat had at least one person educated to degree level, while the figure was 38.4 per cent for households with dogs.

"We don't know why there is this discrepancy," said Dr Jane Murray, a lecturer in feline epidemiology at Bristol University.

The study, published in the Veterinary Record by Dr Murray and her colleagues, aimed to estimate the total number of UK domestic cats and dogs -- as well as identifying the characteristics of their owners.

A telephone survey of households in 2007 randomly selected from the electoral roll revealed that cats and dogs were owned by 26 per cent and 31 per cent of households respectively.

This data was then applied to data from the 2001 UK census -- yielding an estimate of 10.3 million cats and 10.5 million dogs living domestically.

The last peer-reviewed study, dating back to 1989, suggested there were 6.2 millon cats and 6.4 million dogs.

But it is the anomalous difference in degree education between cat and dog owners that has researchers puzzled.

"We did look at average household income but that wasn't significant," Dr Murray said.

"Our best guess is that it's to do with working hours and perhaps commuting to work, meaning people have a less suitable lifestyle for a dog."

"It's really just a hunch though."