Payment processing giant WorldPay is tipped to be the biggest flotation in London this year with a valuation of more than £6 billion.

That comes five years after the business was spun out of Royal Bank of Scotland in a £2bn deal that formed part of its bail-out conditions.

RBS sold its final stake in the company, around 20 per cent, during 2013 for around £160 million. WorldPay is now owned by Bain Capital and Advent.

RBS had bought WorldPay in 2002 and it grew into one of the largest payment processing businesses in the world.

Investment banks Lazard and Goldman Sachs are already working on the details of the stock exchange listing, which could be as early as September.

No-one from Bain, Advent or WorldPay was available for comment.

WorldPay's chairman John Allan recently stepped down to focus his efforts on his position at Tesco.