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) 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), who are handling the sale, he said.

Ed Uzialko, the founder of Lynk, now also a part of RBS WorldPay, told Reuters he wanted to buy the U.S. business back.

RBS confirmed RBS WorldPay is part of global merchant services, one of the assets up for sale, but declined to comment on the specific approach. UBS declined to comment.

RBS WorldPay was valued at about 1.5 billion pounds when it was touted to sellers last year, Ogden said. "We don't know if that's the correct figure today, clearly a lot of due diligence needs to be done," he said.

The business dates back to the establishment of Streamline in 1989. WorldPay, a separate business founded by Ogden, was taken over by RBS through a hostile takeover for about 40 million pounds in 2002.

The enlarged RBS WorldPay business incorporates Streamline and several other companies, including U.S. firm Lynk Systems, which it bought in 2004 for $525 million.

Lynk founder Uzialko told Reuters he was in the early stages of putting together a bid to buy back the business and had spoken to private equity firms about backing and was in the process of hiring an investment bank.

He said in May he was interested in buying it. [ID:nN08515072]