Derek Fincham has a piece " On that funerary statue seized in the UK" and includes a brief rundown of the legal background
The statue was seized after Her Majesty’s Revenue and Customs said the statue was “misdeclared”. It was declared as a statue from Turkey, with an estimated value of $110,000. Yet HMRC alleged the statue originated from Cyrene, Libya and its value was closer to £1.5m. [...]Mr. Al Qassas and his witnesses did not appear to give evidence and to make themselves available for cross-examination. As a result, there was insufficient evidence to challenge HMRC’s argument that the State of Libya owned the statue.A lawyer lobbying for the antiquities trade associations however justifies the practice of misdeclaration of exported antiquities by dealers:
Sometimes foreign sellers misdescribe imports because of fear of theft. It's not to avoid taxes because antiquities come in duty free.But nobody was suggesting it was done to "avoid taxes". And I bet it's not really "sometimes". I also think that taxation is not the problem the exporters and importers want to avoid by misdeclaring the contents of a sealed package or container. But anyway, by Mr Tompa's account, a lot needs to be done to stamp out theft by US postal workers and airport cargo staff.