The Financial Conduct Authority (FCA) said it is looking into the circumstances surrounding a cyber security incident on its US parent’s servers, which has potentially put hundreds of thousands of consumer credit details at risk.

The FCA said: “This statement is made given the public interest in these matters.”

The Rt Hon. Nicky Morgan MP, chair of the Treasury Committee, said: “Hundreds of thousands of people in the UK have been affected by the Equifax data breach. The FCA is right to investigate the circumstances surrounding it. The Treasury Committee will examine this further when it takes evidence from the FCA on 31 October.”

Equifax originally stated that fewer than 400,000 British people were affected, but it has now put the figure at 694,000.

It is believed 637,000 UK phone numbers were stolen, 29,000 driving licence numbers were stolen alongside 15,000 who had some of their Equifax membership details, such as usernames and passwords taken and 12,000 whose email addresses were stolen.

Equifax confirmed in September this year that it suffered a catastrophic cyber-security breach between May and July, prompting questions in a letter from Morgan.

An Equifax spokesperson said: “Equifax Ltd is already working closely with the FCA and other authorities: we welcome this opportunity to learn the lessons from this criminal cyber-attack in order for all businesses to better protect consumers in the future. Cybercrime is a real and ever-present risk faced by all companies, so it is important that Government, regulators and businesses work together to combat this growing threat. We see today’s announcement as a continuation of that process.”

UK customers have been advised to phone Equifax for advice on 0800 587 1584.