Regus Business Centres, which provides office space, support services and technical equipment, will be listed on the London Stock Exchange in October for u1bn.
It is the first time a company of this kind has floated on either side of the Atlantic.
Andy Ryde, corporate partner at Slaughter and May, who is working with corporate assistant Aviad Cobrine on the deal, says: "The company needs constant finance for expansion. We expect there will be no shareholder sales, so it will all be new money. New shares worth up to u250m will be created."
He adds: "There is no other company that provides serviced offices on this scale across a global network. There is little prospect of anyone else in the UK doing this."
Slaughters is advising Regus finance director Peter Jenkins, executive chairman Mark Dixon and company secretary Rudy Lobo.
But Simon Marchant, corporate partner at Freshfields, which is advising Merrill Lynch - the underwriters on the flotation, says: "It is an industry that has been emerging over the last couple of years.
"It would not surprise me at all if others came in."
Jeffrey Oakes and David Wells, both corporate partners at Davis Polk & Wardwell's London office, are heading up the sale of shares in the US, even though the flotation is occurring in the UK.
But, he adds, shares will be sold under Rule 144A which exempts purchasers from the US Securities Act and allows them to trade in UK shares. Although he admits: "There will be complexities."