Children in the UK are illegally using their parents' credit cards and online accounts to rack up huge shopping bills, according to research from CPP.

The card and ID protection firm said that one in five under 16-year olds, or roughly one million children, are taking part in the illicit activity, with 15-year olds the worst offenders.

The research found that the culprits are mostly buying gadgets, games and fashion accessories. The average spend is £25, but CPP said that in some cases children have spent up to £150, and that the activity is costing British parents over £191m a year.

The illegal shopping is taking place because the majority of children know where their parents shop online, while one in five know the passwords and log-ins used on the sites.

CPP said that most parents are in the dark about this activity, and that just two per cent believe that their children might have used their cards and details in such a way. The organisation warned that children are unlikely to conform to online security procedures, and urged parents to keep their cards secure and their offspring in check.

CPP found that 44 per cent of parents bookmark their favourite shopping sites, while a third save their banking details online.

"We are urging parents to be very vigilant with their bank card details, which may check any illicit temptation to shop online," said Michael Lynch, an identity theft expert at CPP.

"Being lax with details online could not only tempt children into making sneaky purchases, but expose parents to the dangers of online fraud. Web fraudsters are getting increasingly sophisticated, and card-not-present fraud is on the rise.

"We are advising people to make sure they log out of sites when finished, to check that shopping web sites are legitimate and to avoid storing credit or debit card details online."