UPDATE 1-Former WorldPay boss keen to buy RBS WorldPay

* Former WorldPay founder says wants to buy RBS WorldPay

* RBS WorldPay could be worth about 1.5 billion pounds

* RBS forced to sell business by European regulators

* Lynk Systems founder also interested in U.S. part (Adds detail, background)

By Steve Slater and Paritosh Bansal

LONDON/NEW YORK, Nov 6 (Reuters) - A founder of part of payment-processing business RBS WorldPay is interested in buying all of the business back from Royal Bank of Scotland (RBS) (RBS.L: Quote, Profile, Research) after European competition authorities told the UK bank to sell it.

RBS WorldPay is one of the leading payment processing businesses globally and could have a price tag of about 1.5 billion pounds ($2.5 billion).

Nick Ogden, chairman and chief executive officer of Voice Commerce Group, said he had backing from up to three private equity firms to finance a deal.

"Yesterday, we formally approached RBS to buy the business back from them," Ogden told Reuters. The interest had been passed on to UBS (UBSN.VX: Quote, Profile, Research), who are handling the sale, he said.