European Union lawmakers are expected to agree on Wednesday to bar bankers in Europe from getting bonuses bigger than their salary, introducing the first cap of its kind globally.
One of the most ambitious reforms of the financial crisis, the cap is designed to address public anger at a bonus-driven culture many European politicians believe encouraged the risk-taking that pulled down banks and governments.
It is set to be introduced from next year despite the objections of Britain. While some token concessions are possible to show goodwill towards the bloc's financial hub of London, the decision on a cap will not be reversed.
EU officials indicated that there could be a further delay to the introduction of the new rules until the middle of 2014 to allow countries time to complete legal preparations - a delay that could spare bankers for one more bonus season.
Lawmakers from the European Parliament and diplomats representing EU countries are to begin talks on finalising the bonus rules at 1730 GMT. Officials expect a deal to be clinched.
"This was a sobering experience," said one official familiar with British thinking, who asked not to be named. "It's the first time the UK was outvoted on financial services.
"There are autopsies being carried out at the UK Treasury. They will only ask for marginal changes but they cannot change the fundamental direction," he said. One European diplomat predicted only "minor tweaks".
The rules, part of a wider capital regime for banks, would limit banker bonuses to the equivalent of their salary, or two times their salary if shareholders agree. They represent the toughest bonus regime anywhere in the world.
They threaten Britain's financial industry the most, raising the risk that some banks and their top bankers could relocate to other financial centres outside the European Union.
Earlier this month, Britain's finance minister, George Osborne, tried to change the rules at a meeting of EU finance ministers but no one supported him.
His inability to fend off the reform underscored Britain's waning influence in the EU and is also likely to fuel deepening euro scepticism in Britain.
The cap has already been softened by allowing banks to discount the future value of share options, bonds or other non-cash payments paid out over more than five years.
As it stands, one quarter of a banker's bonus can be paid in this way but, in an attempt to soften the blow for Britain, this ratio could be raised in the final round of negotiations.
Such alterations, however, would have only a slight impact on the total amount of bonus that can be paid.
Furthermore, any changes will require the approval of the European Parliament, which pushed for the clampdown in a wider law that chiefly deals with increasing the capital that banks hold to make them safer.