‘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 9million 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.