Almost three-quarters of householders in the UK are at risk of losing hundreds of thousands of pounds by unwittingly invalidating their home insurance, a study has shown.

Online insurance search engine Confused.com told Reuters that up to 71 per cent of people run the risk of invalidating their home insurance cover this year without realising it.

That could prove a costly mistake. Insurers could fail to pay out in the event of a building accident - such as a load-bearing wall being knocked out - if policyholders fail to inform them of building work.

They could also turn down claims for theft of contents if householders leave windows open in unoccupied rooms or fail to use locks where fitted.

Debra Williams, managing director of Confused.com, said: "All too often people run the danger of invalidating their insurance because they leave their homes open to opportunist burglars and thieves.

"Forgetting to put tools away, leaving doors and windows open, or leaving expensive equipment out in the garden - even for a couple of minutes - can leave you open to crime without the backup of insurance cover.

"Most people simply don't realise that their cover can be invalidated or reduced, leading to lower levels of compensation, or worse still, no compensation at all."

A total 81 per cent of almost 1,000 householders surveyed conceded they had failed to notify their insurer of building work, while 71 per cent had left windows open in unoccupied rooms.  

Other common causes of insurance invalidation respondents had fallen foul of were giving an inaccurate description of door locks (85 per cent), failing to use an installed alarm (41 per cent) and leaving tools outside or in an unlocked shed (26 per cent).

A further 25 per cent had hidden keys for family and friends to gain access to their home, a fifth left valuables in their garden and 12 per cent failed to report theft to police.