Leading betting exchange Betfair has purchased the customer database of bookmaker Blue Square for STG5 million ($A7.36 million).

The online firm, which was owned by the Rank Group, explains on its website that "Blue Square is now a part of Betfair" and directs its clients towards the Betfair site.

"Betfair Group plc today announces that it has acquired certain assets, including the customer database, of online bookmaker Blue Square Bet for STG5 million," a statement from Betfair said.

"From today, all Blue Square customers will be automatically redirected to Betfair where they can access a full suite of sports betting and gaming products and receive a promotional welcome offer.

"The acquisition is consistent with Betfair's strategy of focusing on regulated markets and growing its sportsbook and gaming operations alongside the exchange."