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A brand new class has been approved for firms traded on the London Stock Exchange, which can permit oil big Saudi Aramco to checklist shares in London.
London has been accused of watering down corporate governance rules to be able to accommodate the large listing.
The Institute of Directors stated the transfer put the "UK's global reputation as a leader in good governance" in danger.
London is vying with New York for the state-owned oil agency's listing, anticipated to be the world's largest.
The proposed share flotation will see 5% of the state-owned firm offered in an Initial Public Offering.
Aramco has but to verify the place, or certainly if, it'll float the shares, with some reviews it could as an alternative shelve the flotation in favour of personal share gross sales.
The City watchdog stated there was "considerable benefit to investors" from the rule change.
"These rules mean when a sovereign controlled company lists here, investors can benefit from the protections offered by a premium listing," stated Financial Conduct Authority chief govt Andrew Bailey.
However, the Institute of Directors stated it was "deeply disappointed", calling the transfer "a reduction in standards".
The Investment Association stated it was happy some investor issues had been mirrored within the finalised rules, nevertheless it continues to oppose the inclusion of firms within the new class in main fairness indices such because the FTSE 100, as this may pressure UK savers to spend money on them.
"Savers must have confidence that a company is run for all shareholders," the Investment Association's chief govt Chris Cummings stated.
Mr Cummings also stated that he anticipated the FCA to overview the brand new class after two years.
TheCityUK, a membership organization for London's monetary sector, deemed the rules "the product of a thorough and transparent process", including that it was "key" that the FCA ought to overview the choice "in a timely manner".
Mohammed bin Salman, Saudi Arabia's Crown Prince, has proposed an Aramco share sale as a part of his financial reform agenda.
A sale is a part of wider plans to assist the nation ease its dependence on oil exports.
Companies will be capable of search admission to the brand new class on the London Stock Exchange from 1 July 2018.