The British government has reportedly launched a detailed investigation into Bernie Ecclestone's tax affairs.
Last year, amid speculation the Gerhard Gribkowsky corruption probe had piqued the interest of the UK's Revenue and Customs (HMRC) department, a spokesman said it was ensuring "everyone pays the right tax under the law".
It was reported that the government would pay particular interest to the F1 chief executive's offshore family trust, which he insists is outside his control.
The Daily Mail newspaper now reports that, on the basis of the informal investigation, an official probe could be launched that might cost Ecclestone billions in tax.
"HMRC has put a team of investigators on Bernie Ecclestone to look into his involvement in the trust and exactly how much he has to do with it," an official is quoted as saying. "They are now in the process of making enquiries and researching every minor detail as they look to build a case. There is movement. They have opened a book."
Bernie Ecclestone played down the report, "I have not received any correspondence from HMRC and don't anticipate any. There is no reason for it. As far as I am concerned, if they write to us, we will reply, but I hope I don't get a knock at the door in the night. I received a letter from HMRC in 2008 that everything was ok in relation to the trust. It would be silly to check again when they have already said everything was in good order."
HMRC declined to officially comment.