They are investigating 15 recent cases of offenders entering properties through insecure doors and windows and stealing items that have included handbags, purses, cash, jewellery, keys and a laptop computer and games console.

Sgt Simon Wilson, of the Northallerton Safer Neighbourhoods Team, said the majority of the incidents occurred between 6pm and 10pm.

"These criminals are highly opportunistic and are clearly targeting properties where owners are in and out of their gardens and are failing to lock doors and close windows when they go back into the house," he said.

"Whilst the police does everything it can to catch the offenders, it is essential that homeowners wise up to the fact that their property and possessions are wide open to sneak-in burglars if their home is left insecure.

"Even if you're sitting in the living room watching television, don't be lulled into thinking you won't become a victim simply by your presence.

"It only takes offenders a few seconds to open a door or reach through a window and you could be hundreds or even thousands of pounds out of pocket, especially if your car keys are taken."

Sgt Wilson said light summer evenings were a big factor in these incidents, particularly as people seem to be more lax about security, with some even forgeting to lock-up altogether before going to bed.

"I urge residents to be more mindful and take every precaution to deter the burglars," he said. "As always, the most basic but effective advice is to keep doors and windows secure at all times.

"By removing the opportunity you will go along way to preventing the burglary."

Anyone with information about the burglaries in Northallerton or any suspicious activity to report, is asked to contact the Northallerton Safer Neighbourhoods Team on 0845 60 60 24 7 or call Crimestoppers anonymously on 0800 555 111.