TCS

The Indian IT worker based in London has an M&S email address but is a paid TCS employee.

TCS has previously said it is investigating whether it was the gateway for the cyber-attack.

M&S and TCS have both declined to comment.

It is not clear when TCS launched its investigation.

TCS says it has over 607,000 employees across the world and is the lead sponsor of three prestigious marathons - New York, London and Sydney.