The UK's Office of Fair Trading (OFT) is extending its probe into the interchange fees charged by Visa and MasterCard to include "immediate" debit card transactions.
The OFT is already investigating MasterCard and Visa's current UK interchange fee arrangements relating to consumer and commercial credit cards, charge cards and deferred debit cards.
The investigation will now include "immediate debit cards".
The watchdog has been investigating interchange fee arrangements in the UK since 2000 and has described them as "a tax on UK consumers".
The watchdog says the expansion of its current probe is consistent with the scope of the European Commission's current investigation into MasterCard's European intra-regional interchange fees. In June last year the EC formally charged MasterCard with breaking antitrust rules and restricting competition between banks by pre-determining interchange fees charged for cross-border card transfers.
But despite it's on-going investigation, the EC did not recommmend overhauling the controversial fee structure in its report on the European retail banking markets which was published last week.