More than two million Britons regularly leave their homes unlocked when they go out and 17 million householders do not lock up when they are at home, according to research from insurer Halifax.

Householders take the least care with the back door with 1.3 million people leaving it unlocked even though police figures show one-in-four successful burglaries involve criminals gaining access via an unlocked door.

In a poll of 1,168 adults, some of the reasons given for not locking-up were: a belief neighbours were keeping an eye out – 18 percent, a belief the area had a low crime rate – 18 percent and just plain forgetfulness – 10 percent.

"With street crime rising by 8 percent 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," said Vicky Emmott, senior underwriter at Halifax Home Insurance.

"But judging by the findings of our report, millions of Britons still live in the past," she said in a statement.

She said the best advice was the simplest – lock external doors even when at home.