Householders take the least care with their back door, as 1.3 million people regularly go out leaving it unlocked.
Responding to its findings, Halifax Home Insurance warns householders that external door provides the entrance point for 68 per cent of burglaries.
Furthermore, that one in four burglaries involve a thief entering a property through unlocked external doors.
Vicky Emmott, senior underwriter at Halifax Home Insurance, said: With street crime rising by 8 per cent this year the idea that any street in Britain is safe enough for you to leave your door unlocked is little more than a nostalgic notion.
Ensuring that all external doors are locked when a property is unoccupied is a simple but crucial step to reduce the risk of burglary. Indeed many burglars will spend no longer than 60 seconds trying to break into a home.
Reasons given for leaving doors unlocked when out of the property included; a belief that neighbours were watching the property, perceiving the area they lived in as having low crime and simply forgetting to lock doors.
Up to 3 per cent leave their door unlocked because they feel that they dont have anything worth stealing, but reformed burglar, Bob Turney, now a probation officer, disagrees.
He said: The average household contains around £3,000 to £5,000 worth of items that are easy to steal such as laptop computers and mobile phones.
More than 15 million Britons also think its safe enough to leave an external door unlocked whilst inside the home, and do so in the belief that their presence is enough to make their secure.
Contrary to this notion, Halifax Home Insurance points out that 55 per cent of burglaries take place while a resident is still inside the home.
Vicky Emmott said: Locking doors is such an effortless action and yet it probably provides the most effective deterrent to any thief. Householders should be aware that leaving a home unlocked when its unoccupied could invalidate a home insurance policy leaving the homeowner to pick up the pieces alone.
Householders should also be increasingly aware of the security risks of leaving doors unlocked even when they are in the home, especially since todays burglars seem less worried about whether you are in or out. The simple rule is to keep all external doors locked at all times.
