Margaret Hodge, the chair of the Public Affairs Committee has said the HMRC are "behind the times" when it comes to tax avoidance schemes.
Speaking to Daybreak she said it was a "cat and mouse game", with those who exploit legal loopholes, always one step ahead.
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The PM confirmed an end to the country's existing trading arrangements as she outlined her 12 priorities for negotiating Britain's EU exit.
Theresa May has pledged to invoke Article 50 by the end of March, beginning the Brexit process. Here is an A to Z of what you need to know.
A judge said those bringing the case can remain anonymous after they said they feared for their safety if their identities were revealed.