Britain's Labour opposition leader launched an offensive against banks on Sunday ahead of his party's annual conference, promising a "real separation" of retail and investment banking and to raise the top rate of personal income tax.
The Conservative-Liberal Democrat coalition government has said it will implement the recommendations of an independent review by Oxford University economist John Vickers into how banks should be structured in the wake of the global credit crisis.
But critics, including Vickers, have lamented the watering down of some of the proposals - including the definition of the ring fence between retail and investment arms and the ratio of loans to capital that banks can hold on their books.
Britain's banks - including Barclays, RBS, Lloyds and HSBC - will have until 2019 to make the changes with the government committed to write the new rules into law by 2015.
Labour accuses the government of caving in to fierce lobbying by the financial sector.
"Either they can do it themselves - which frankly is not what has happened over the past year - or the next Labour government will, by law, break up retail and investment banks," Labour leader Ed Miliband said.
"The banks and the government can change direction and say that they are going to implement the spirit and principle of Vickers to the full - that means the hard ring-fence between retail and investment banking. We need real separation, real culture change. Or we will legislate."
Some in the Conservative-led government had been concerned that punishing the financial sector could damage the competitiveness of the City of London, a major global financial center, and potentially harm a crucial part of Britain's recession-hit economy.
Miliband's warning to the banks comes ahead of his party's annual conference in the northern English city of Manchester, where he is under pressure to explain to voters how it would govern if elected in 2015.
Miliband, who replaced former prime minister Gordon Brown as Labour leader after that defeat, has struggled to make a good impression on voters so far. While opinion polls show Labour would win an election tomorrow, his own personal approval ratings languish below those of Prime Minister David Cameron.
Seeking to capitalize on a perception of Cameron's government as too friendly to the wealthy in an era of austerity, Miliband said Labour would reverse a tax cut for the highest earners in this year's budget which saw the highest rate of income tax drop to 45 percent from 50 percent.
(Editing by Patrick Graham)