Home Secretary Amber Rudd has been warned she faces "serious questions" after leaked documents revealed that she used to be director of two offshore companies.
Details of Ms Rudd's involvement were included in a cache of 1.3 million files obtained by the German newspaper Sueddeutsche Zeitung and shared with the International Consortium of Investigative Journalists (ICIJ).
There is no suggestion of wrongdoing by the Home Secretary, but opposition politicians insisted that she had questions to answer.
Papers seen by The Guardian and BBC Panorama show that between 1998 and 2000, Mrs Rudd was director of Advanced Asset Allocation Fund and Advanced Asset Allocation Management.
The companies were among 176,000 listed as having been set up in the Bahamas, which was last year named by the EU as an unco-operative tax haven
Earlier this year, Ms Rudd defended then Prime Minister David Cameron after his father's offshore fund featured in the separate Panama Papers leak. She said then that "international transparency on tax matters is essential".
A spokesman for the Home Secretary played down the significance of the leak, saying : "It is a matter of public record that Amber had a career in business before entering politics."
But Labour shadow minister Jon Ashworth said: "It's embarrassing for Theresa May's Tories that another senior figure has been linked to revelations about offshore tax havens.
"Earlier in the year Amber Rudd was sent out to defend David Cameron amid controversy over offshore holdings.
"At the time she trumpeted transparency yet she made no mention of her own situation, which was surely relevant to claims amid calls for openness at the top of the Tory Party.
"People will be forgiven for wondering what the true picture is and they deserve an answer from Amber Rudd."
And Liberal Democrat leader Tim Farron said: "Serious questions for Amber Rudd - she must provide clarity. The public are sick of the idea of politicians tying to dodge the rules they make."
Green MEP Molly Scott Cato, a member of the European Parliament's inquiry into the Panama Papers, said: "During her brief leadership campaign Theresa May made clear that she would lead a government 'that works for everyone' and would encourage a more ethical approach to business.
"In this context it is difficult to see how she can continue to have confidence in Amber Rudd as Home Secretary. The Prime Minister needs to take firm action to lay to rest fears that the UK may turn into a tax haven following our withdrawal from the EU."
Meanwhile, the European Commission was facing questions over the presence of its former competition chief in the leaked documents from the Bahamas corporate registry.
Neelie Kroes, who was competition commissioner between 2004-10, is listed as director of an offshore company registered in the Bahamas. It is understood she has told the Commission she did not declare the post because the company never became operational.
Carl Dolan of anti-corruption group Transparency International said: "It is incredible that something like this - which is a clear breach of the rules and could have led to a major conflict of interest - was undetected by the European Commission for so many years."
But the Commission's chief spokesman Margaritis Schinas told reporters: "There are certain things that even the strictest rules can't fix."
In the future, the Commission "will make sure that memory doesn't fail here when it comes to declarations of interest", he said.