Network Rail's railway arch property portfolio has been sold to Blackstone Group and Telereal Trillium for £1.46b.
National Rail said Telereal and Blackstone will hold equal ownership stakes, of which they intend to be long-term owners.
Ahead of the sale a group called Guardians of the Arches was established to represent the thousands of businesses that operate in railway arches. It wrote to transport minister Jo Johnson asking him to protect their interests, fearing dramatic rent increases.
Graham Edwards, co-founder and chairman of Telereal, said: "The arches portfolio is a unique and vital part of the UK economy. We are tremendously excited by the prospect of working with its entrepreneurial tenant base - made up of car mechanics, bakeries, micro-breweries, restaurants and just about every type of business you can think of. These tenants are a vibrant part of many local economies and communities.
"As a long-standing real estate investor in the UK, we and our partner Blackstone believe that our ownership of the portfolio will provide the supportive environment in which these businesses can flourish on a long-term basis. For example, our business plan anticipates investing in several hundred currently disused arches so that they can provide space for more local businesses.
"With our permanent capital structures, we will be investing in the portfolio for many years. We believe that the long-term success of this portfolio rests on strong relationships with our tenants, as well as with local communities and local government. We intend to remain particularly sensitive to the small businesses that have been long-term tenants of the Network Rail estate, and look forward to a long-term partnership with Network Rail."
David Biggs, managing director of Network Rail Property, said: "We are proud to have fostered so many small, independent, diverse businesses and communities across the country and we are confident that these will continue to thrive under the new owners.
"Ultimately our role is to run, improve and grow the railway, and managing these properties isn't essential to that. The new owners will invest in and grow the estate, and we can focus on our core business of running the railway."