The Financial Services Authority (FSA) has refused to name the companies behind more than 300 adverts it removed last year.
The regulator banned a total of 327 financial adverts in 2011 after removing 262 the previous year, but it has not answered calls from consumer group Which? asking the FSA to name the adverts and the organisations behind them.
Which? obtained the data under the Freedom of Information Act.
The Financial Conduct Authority (FCA), one of the two authorities set to officially replace the FSA next year, will be given the powers to name companies behind banned adverts.
"We are pleased that the FCA, unlike the FSA, will publish details, including the name of the company, when it has found a dodgy financial promotion.
"Our findings demonstrate why this new approach is important - 300 adverts have been removed but no-one knows which companies and products they were promoting," Which? said in a statement.
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