Police in Britain have launched an investigation into a ransom demand received by telecoms company TalkTalk after the company suffered a major cyber attack.

The company has revealed it was contacted by somebody claiming to be responsible for the cyber attack, which may have seen hackers steal sensitive customer data.

A TalkTalk spokeswoman said: "We can confirm we were contacted by someone claiming to be responsible and seeking payment," adding: "Everything else is a matter for the police."

A spokesman for Scotland Yard's cyber crime unit, which is investigating the data breach, said: "We are aware of this information and it will form part of our investigation."

A "significant and sustained" attack on the firm's website earlier this week means credit card and bank account details may have been stolen.

TalkTalk says customer names, dates of birth, addresses and phone numbers may also have been accessed.

The company's four million customers are being urged to check their accounts for any suspicious activity "over the next few months" and change their passwords.

TalkTalk boss Dido Harding said the company was taking the attack "extremely seriously", and stressed it was not certain what information had been stolen.

She said: "I'm sorry to be so vague, but at this stage we're not certain what information has been stolen.

"We're taking the precaution of contacting all of our customers because there is the potential that bank details and credit card details have been stolen, but at this stage I can't be certain that's the case."

The breach is the third in a series of cyber attacks that have affected TalkTalk customers.

In August, the firm revealed its mobile sales site was hit by a "sophisticated and co-ordinated cyber attack" in which personal data was accessed.

In February, customers were warned about scammers who managed to steal thousands of account numbers and names from TalkTalk's computers.