The Financial Conduct Authority suggested in a public consultation discussion paper in May that Britain's twin-track listings regime could be merged into a single entry point to attract more start-ups. It also suggested raising the threshold for requiring shareholder approval for big transactions.

After Brexit cut off the City of London from the European Union and a decision by UK chip designer ARM to list in New York, there have been calls for a revamp of listing rules to keep Britain globally competitive in capital markets.

Railpen and nine other UK pensions schemes which oversee 300 billion pounds ($379 billion) in assets, said in a letter to the FCA on Wednesday that the proposals need a "broad and evidence based policy discussion".

"Proponents of a more relaxed UK approach to shareholder rights underestimate the extent to which investor-friendly corporate governance standards have shaped the UK's attractiveness on the world stage," said Caroline Escott, senior investment manager at Railpen, said in a statement.

Church of England Pensions Board, HSBC Bank (UK) Pension Scheme, and the Universities Superannuation Scheme were among the letter's signatories.

The Principles for Responsible Investment (PRI), which campaigns for responsible investment, said it strongly opposed the FCA's suggestions which could deter early-stage companies and remove mandatory shareholder votes.

"The UK serves as a global reference on corporate governance, and relaxation of existing standards can have a ripple effect on corporate governance practices globally," PRI said in a statement.

The Investment Association, which represents asset managers, said in its response to the FCA consultation, which closed on Wednesday, that it welcomed the watchdog's blueprint for significant reform to bolster UK competitiveness.

"Overly restrictive Listing Requirements have acted as one of several reasons why some companies have listed elsewhere," the IA said.

($1 = 0.7913 pounds)

(Reporting by Huw Jones;Editing by Elaine Hardcastle)

By Huw Jones