The believed presence of a “skimmer” fraud device on at least one ATM operated by HSBC bank is under investigation.

An HSBC spokeswoman last night declined to state how many machines might have been affected but said the bank was “working closely with the police to resolve these attacks”.

She added: “The investigation is ongoing and we will notify affected clients or their banking institution as more information becomes available.”

Customers were advised to notify the bank if they spotted any suspect activities while reviewing their transactions.

Skimmers are illegally fitted to cash machines, enabling fraudsters to obtain information from debit cards.