Like a Thief in the Night: British Museum Involved in Clandestine Movement of Cultural Property?

The Art Newspaper reports ('Secret flight path of the Parthenon statue') that when the British Museum unexpectedly lent support to Vladmir Putin's regime during the Ukraine Crisis in late 2014 by lending a  sculpture pulled off the Parthenon to the State Hermitage Museum

there were fears that Greece might try to seize the statue en route to St Petersburg. To prevent this, the loan was shrouded in secrecy until the sculpture of the river god Ilissos went on show in the Hermitage (6 December 2014-18 January 2015). The Art Newspaper has learned that the route it took was designed to avoid European Union territory as an extra precaution. Mikhail Piotrovsky, the director of the Hermitage, tells us that to forestall any attempt to intercept the sculpture, it was flown from London to St Petersburg “circuitously”. He says: “It could not be transported through Europe, because Greece [...]  could have attempted to seize it at some airport en route, and according to the laws of the European Union, this would have been legitimate.”

So look where they'd have had to take it to get it out of the UK and into Russia without passing through any intermediary point. That is how certain the BM are of their "collectors' rights".