Cyber criminals said they were using the details to demand a ransom for the Kido nursery chain, which has 19 UK sites - 18 in Greater London and another in Windsor.

Experts have condemned the hack as an "absolute new low" for cyber-crime.

Cyber criminals said they were using the details to demand a ransom for the Kido nursery chain, which has 19 UK sites - 18 in Greater London and another in Windsor.