Owners who use the services of commercial dog walkers have been warned they could find themselves in court if their pet is not kept under control.

The warning comes after a man was fined for failing to stop his Dogue de Bordeaux attacking a Samoyed on Hampstead Heath – despite the fact the dog was being walked by someone else.

The Samoyed needed £5,000 worth of treatment after suffering severe bite injuries to the stomach in the attack on December 2 last year, and it had to be kept in a veterinary hospital for two weeks.

Richard Gentry, the head of Hampstead Heath Constabulary, said: “If you’re unable to keep control of your dog in an open space, you need to understand the ramifications.”

Jonathan Till, of Lismore Circus, Gospel Oak, was ordered to pay a fine and court costs of £700 for allowing his dog to be dangerously out-of-control on the Heath.

He did not attend the hearing at Highbury Corner Magistrates’ Court but was convicted in his absence.

The dog was actually being walked by Joseph Beveridge, of Fleet Road, Gospel Oak, who was ordered to pay £375 after pleading guilty to the same offence.