Payments processor Worldpay has listed on the London Stock Exchange in an initial public offering valuing the company at £4.8 billion.

It is the biggest flotation in London this year.

Shares in Worldpay were trading at 255 pence in early trading, up five per cent and above the 240 pence offer price. One source familiar with the matter said demand outstripped the number of shares on sale by six to seven times.

Worldpay's private-equity owners Advent International and Bain Capital were reported to have rejected an offer of up to £6.6bn including debt, earlier this year from French rival Ingenico Group SA.

Including debt, the initial public offering (IPO) values Worldpay at £6.3bn.

Advent International and Bain bought Worldpay from Royal Bank of Scotland in 2010 for about £2bn. The business provides platforms to allow merchants to accept payments by cards and other methods.

Worldpay processes about 31 million mobile, online and in-store transactions every day and has about 4,500 staff, mostly in Britain and the United States, its two biggest markets.

"We have already invested over £1 billion in our technology, people and capabilities, helping us to become an advanced and sophisticated technology-led organisation with great potential," chief executive Philip Jansen said.

Worldpay's private equity owners had narrowed the price range for the IPO to between 235 pence and 250 pence from 225 pence to 260 pence last week.

A bookrunner for the deal said earlier this month that Worldpay was seeking a valuation of between £4.5bn and £5.2bn.

Worldpay said the IPO would raise £2.16bn, with the company receiving £948 million. Worldpay's private equity owners will hold on to about 49 per cent of the company's shares.

London has seen fewer firms go public this year, with 93 listings raising about £5.3bn pounds by September 30, roughly half the £11bn raised from 136 listings in the same period last year, according to stock exchange data.

Merrill Lynch, Goldman Sachs and Morgan Stanley acted as joint global coordinators for the Worldpay IPO. Lazard acted as financial adviser to the company.

Worldpay made underlying earnings before interest, tax, depreciation and amortisation of £375m last year, up from £346m in 2013.