Payments and cashpoint giant VocaLink is being sold to Mastercard in a deal worth up to £869 million.
Mastercard is snapping up a 92.4% stake in UK-based VocaLink for £700 million, with a further potential £169 million due if performance targets are met.
VocaLink runs services for banks, including Bacs, Faster Payments and Link cashpoints, as well as mobile app Zapp.
It is owned by a group of 18 banks, including HSBC, Royal Bank of Scotland, Lloyds Banking Group and Barclays.
The deal comes after the Payment Systems Regulator called in February for banks to sell their stake in VocaLink to "open the market and allow for more effective competition and innovation".
It said at the time that banks should loosen their grip on the way payments are processed, with VocaLink processing more than 90% of salaries, over 70% of household bills and almost all state benefits in the UK.
The banks will retain a 7.6% stake in VocaLink for at least three years.
Taxpayer-backed lender Royal Bank of Scotland is one of the largest shareholders in VocaLink, with a 21.4% stake, and said it will see a profits boost of around £150 million initially.
Barclays confirmed it is set to gain up to £133 million from the sale for its 15.2% stake, while the Co-operative Bank will get up to £28.3 million for its 3.3% shareholding.
Ajay Banga, president and chief executive of Mastercard, said: "We're excited about the opportunity to play a bigger role in payments in the UK, a very strategic market for us.
"VocaLink is a unique company with outstanding technology, assets and people."
David Yates, chief executive of VocaLink, who will join the Mastercard management committee after the deal, said: "We will continue to focus on ensuring that the UK systems perform seamlessly.
"At the same time, we'll invest in further innovation to power competitive payments solutions for consumers and businesses around the globe," he added.
Banks including Barclays founded Voca and LINK in 2003, which later merged to form VocaLink.
It processed more than 11 billion transactions last year with a value of £6 trillion.
As well as powering the Faster Payments Service on behalf of the Faster Payments Scheme, the Account Switching platform, Bacs and the Direct Debit Scheme, VocaLink also connects more than 70,000 cashpoints through the LINK scheme.
It reported revenues of £182 million in 2015.
Chancellor Philip Hammond said the VocaLink deal " shows that Britain remains an attractive destination for international investors".
He added: "The Payment Systems Regulator recommended the UK's biggest banks sell their stakes in VocaLink to improve banking competition in the UK which will deliver clear benefits for challenger banks, fintechs (financial technology companies), UK consumers and small businesses."