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]

Voice Commerce Group's Ogden said he expected other interest in the business, but was optimistic that his financial backing, knowledge of the firm and support from staff and customers would give him an advantage.

Brussels has given RBS up to four years to sell its assets.

RBS Chief Executive Stephen Hester on Friday said on asset sales: "The telephones are ringing, but don't expect anything soon. You should expect it to take at least a year before the first of these businesses goes anywhere."

RBS, now 84 percent owned by Britain, on Friday reported a third quarter loss of 1.5 billion pounds. [ID:nL6671701]

Ogden of Voice Commmere Group said a rapid deal would be beneficial, including for RBS.

"The reality is we're already being approached by many of their large customers, not through any predatory approach but because their customers are moving," he said.

Voice Commerce Group provides mobile financial, payment, identity and verification services, and may be worth between 100 million and 200 million pounds, Ogden estimated.

"Clearly the partnership with private equity companies is key to this (interest in RBS WorldPay)," he said.

RBS WorldPay includes Bibit, Payment Trust and RiskGuardian in addition to WorldPay, Streamline and RBS Lynk.

It operates in more than 40 countries and processes about 4.4 billion transactions annually, or 12 million each day, according to its website. Streamline handles almost half of all UK transactions. ($1=.6025 Pound) (Additional reporting by Kate Holton in London; editing by Karen Foster)