Scientists have claimed the idea that dogs age seven years for every one human year is a myth.

University of California researchers say they have also found puppies are middle-aged by the time they are two, though dogs tend to age more slowly than humans in later life.

By the time they get to three - and are possibly still getting away with things due to being considered young - dogs are closer in age to a 50-year-old human.

The study looked at how dogs aged by focusing on the DNA methylation in 104 Labradors aged between 4 weeks and 16 years.

The DNA contains marks that change over time as a cell matures, allowing scientists to track the animal's biological age.