Reqs the investigation dog is putting his paws up and heading into retirement from the Hertfordshire Fire and Rescue Service.

The black Labrador has attended about 500 incidents since joining the service in 2012 as a one-year-old, and the service says he is Britain’s longest-serving fire investigation dog.

Reqs has used his brilliant sense of smell to sniff out substances like petrol at incident scenes, and helped fire investigators like his handler, Watch Commander Nikki Harvey, to find crucial evidence in a range of cases.

These have included high-profile investigations such as arson and murder, and led to more than 250 years of imprisonment for convicted offenders, according to the service.

Ms Harvey said: “We are called to the scene of any serious fire that crews believe to be deliberate or suspicious, or where the cause is not immediately known, especially if there has been a fatality at the scene.

“Reqs gets involved as soon as it is safe.

“I’ll go through the scene first to check that it has properly cooled down with no visible sign of smoke or embers and that there aren’t any hazards that could harm him.

“He gets to work using his best tool, his nose, to locate any potential accelerants like petrol that might have been used to deliberately start a fire.

“That’s when the human fire investigators like myself can take a closer look while Reqs enjoys a reward, his favourite tennis ball.”

Reqs, who will enjoy his retirement as Ms Harvey’s pet dog, will be succeeded by his protege Loki on the fire and rescue team.

Ms Harvey has promised that Reqs will not become a stranger to Hertfordshire residents.

Regular appearances at fire station open days, along with school and club visits and the comfort he has brought to many families who have sometimes lost everything in a fire, have made him a firm favourite with people.

Ms Harvey said: “His interactions with children, especially those who have had fire in their home, leaving them quite frightened, can be therapeutic.

“The distraction of stroking him and throwing him a ball can give comfort and reassurance to those affected by traumatic incidents.”

She added: “I’ll miss the nice cuddles he gives at the end of a job, especially if we’ve been to an upsetting or distressing incident.

“He’s my best mate and I love him to bits – while it’s the end of an era in some ways I’m so pleased he’ll still be around and part of our very special community, and I know that Loki will carry on doing a great job in his paw-steps.”