Shares of payment processing firm Worldpay Group, sold by RBS to comply with EU rules after its UK state bailout, rose 28% on Tuesday after Worldpay said it received preliminary approaches from US firms Vantiv, Inc and JPMorgan Chase.

Worldpay shares rose to around 408p to give it a current stock market value of around £8.1 billion.

RBS sold a majority stake in Worldpay to Bain Capital and Advent International in 2010 and the private equity firms took Worldpay public in October 2015 at 240p per share, according to Bloomberg data.

“The board of Worldpay Group plc notes the recent press speculation concerning Worldpay and Worldpay share price movement and confirms that it has received preliminary approaches from Vantiv, Inc and JPMorgan Chase Bank in relation to the potential acquisition of the entire issued, and to be issued, share capital of Worldpay,” said Worldpay in a stock exchange statement.

“There can be no certainty either that an offer will be made nor as to the terms of any offer, if made.”

Vantiv and JP Morgan must now either announce a firm intention to make an offer for Worldpay by August 1 or announce that they do not intend to make an offer.