Payment processing company Worldpay has announced plans for a stock market float next month which could give it a market value of close to £4 billion and propel it into the FTSE 100 Index.

The group said it would offer shares in London in a move which will reportedly give the company an overall value of around £6bn, though this includes £2.2bn of debt.

It means the company has preferred to go ahead with a flotation rather than a reported £6.6bn takeover approach by French rival Ingenico.

UK-based Worldpay was carved out of state-backed Royal Bank of Scotland in 2010 when private equity firms Advent and Bain snapped it up for £1.7bn.

They have since invested more than £1bn in the company which has added 2,500 employees and now has a workforce of around 4,500 in 11 countries. Most of the jobs are in the UK.

Worldpay processes about 11.5 billion transactions every year totalling around £370bn, through around 400,000 merchants. It says on a typical day this represents 31 million mobile, online and in-store transactions, covering 146 countries.

In 2014 net revenue was £863.4m and underlying earnings £374.7m. In the first half of this year, revenues were up 13 per cent to £465.7m and earnings by 13 per cent to £182.6m.

The group sees prospects for growth fuelled by a rise in non-cash payments, expected to increase by 7.3 per cent a year to 2019, three times the rate of cash. It also sees fast growth in online and mobile payments and rapid expansion in emerging markets.

Its float is expected to see at least 25 per cent of stock trade publicly with the initial public offering (IPO) set to raise around £890m. The move is designed to support the company's growth plans and help reduce debt.

Chief executive Philip Jansen said: "Worldpay has been transformed into a global leader in payments since it became an independent company in 2010. We have built a modern and sophisticated technology-led organisation with huge potential.

"The IPO is an exciting and logical next step as we seek to continue this momentum."

Chairman Sir Michael Rake said: "Worldpay is a leader in the extremely dynamic world of digital payments having been a pioneer in card payments, multi-currency processing, online payments and contactless technology."