Guardian News and Media/London

Labour will refer the high street banks to the competition authorities immediately if it is elected in 2015, Ed Miliband is expected to say in a centrepiece speech on banking reform today.

The party leader wants the proposed review by the Competition and Markets Authority (CMA) to complete within a year of the election, and anticipates it could lead to a breakup of the larger high street banks, such as RBS or Lloyds.

He is expected to argue that greater competition in financial services is central to restoring Britain’s long-term economic prosperity and providing consumer choice.

The intention would be to give greater choice for consumers and to address obstacles preventing new players from breaking into the market.

One proposal is a cap on market share on the largest banks, but the party would not indicate whether it had a specific cap in mind.

Labour officials would only say that a market share cap of 25% - as had been suggested in a leak on Tuesday night - was wide of the mark.

The Miliband speech aims to show that he can develop his successful, but arguably fully mined, living standards agenda into policies that offer a wider route map to greater economic prosperity. He also hopes to exorcise Labour’s reputation for having left the City of London insufficiently regulated during its time in office.

But the party leader suffered an immediate political setback when Mark Carney, the governor of the Bank of England, said he was opposed to crude caps on the size of market share for banks.

Giving evidence to the Treasury select committee, a sceptical-sounding Carney told MPs: “Just breaking up an institution doesn’t necessarily create a viable or more intensive competitive structure.”

In an attempt to set the scene for his economic speech, Miliband tried in parliament to wrongfoot David Cameron by demanding that the prime minister prevent state-owned RBS to award bonuses to bankers worth up to twice their annual salaries. The European Union has said that if a bank wants to award a bonus to double a banker’s basic salary it should be subject to a shareholder vote, although the proposal is being challenged by the Treasury on the grounds that it creates perverse incentives by removing the link to performance.

Cameron tried to sidestep the issue of the future size of RBS bankers’ bonuses by saying there would be no increase in the overall RBS bonus pool this year. He said that Miliband had “all the moral authority” of the Rev Paul Flowers, the disgraced Co-op banking chief, given the last government’s record on banking regulation. Downing Street said the total package of pay and bonuses at RBS had halved under the coalition government, from £3bn in 2009 to £1.4bn in 2012.

Labour retaliated by saying this was a red herring.

Chris Leslie, shadow chief secretary to the Treasury, said: “The house needs to know that RBS has been reducing the number of bankers on their roll by about 2,000 bankers in the last year. You’d expect their total pay bill to actually start to fall. So it should.”