The directive forces deposits held by UK residents in offshore EU jurisdictions, such as Jersey, to be declared to the UK authorities or face a tax charge.

Last week, Jersey announced that it had levied £13m in retention taxes as a result of the directive.

Tax campaigner Richard Murphy said that more than £100m should have been collected based on his analysis of Jersey figures of UK deposits on the island.

'Funds must be held in entities owned by individuals in the UK and EU to which the EU savings tax directive would not apply, such as trusts and companies,' he said.

The use of trusts has been especially controversial, since the UK Treasury took the view that trusts were outside the scope of the directive, which campaigners believe will open the way for further evasion.

A spokesman for the Jersey authorities cast doubt on the analysis, saying that only a third of the Jersey deposits would be personal, and many would relate to companies.

'We don’t subscribe to the view that there is evasion through trusts. A trust is not an inexpensive thing to set up. It’s not cost effective for small depositors,' he said.

A Treasury spokesman said that the operation of the directive was being 'carefully monitored'.