Scientists from the Royal Veterinary College analysed the medical records of 150 000 dogs expecting to prove the conventional wisdom that selective breeding makes pedigrees more vulnerable to serious conditions such as heart murmurs and joint problems.

But, to their surprise, it turned out that mongrel and pedigree dogs have broadly the same chance of developing the most common health problems.

In fact, in the case of degenerative joint disease, mongrels were found to be more vulnerable. Of the 20 most common conditions, only ear infections, obesity and skin growths were observed to be any more common for pedigree animals.

The data was gathered from 100 vet practices in the Midlands and South East of England over the past five years, the Sunday Telegraph reported.

Dr Dan O'Neill, who led the study, told the newspaper: “The outcome is that there is not strong or convincing evidence of a difference between purebreeds and crossbreeds in their health.

“There is this image of crossbreeds as paragons of health. In fact they are just crosses of purebreds, with combinations of prevalences you find in their parent. It is not that they are healthier overall, and it is wrong to stigmatise purebreds.”

Estimates suggest that around three quarters of Britain's 9 million pet dogs are pedigrees.

The 150 000 dogs studied included mongrel dogs as well as selectively-bred crosses such as labradoodles and cockerpoos, but did not suggest a difference in their overall health.

Although the chances of a given dog developing diseases was not affected by the purity of their breed, the data did reveal that crossbreeds on average live a year longer than pedigrees - to 13 instead of 12.