It's a very grey area.
When Princess Margaret died,she left all her jewels to her two children.
Not that long ago they sold them(much to the annoyance of Lord Snowdon).
It seems many of these were paid for (out of the Civil List) by the Queen,so perhaps we can argue that the money should have gone back to the Queen,or to the taxpayer.
The problem is,there is (now) no way of knowing(apparently) which jewels were bought privately,and which were bought with(in effect) taxpayers money.
If we cannot decide this for jewels bought around 1961,how are we to make a decision on jewels going back to 1936 and beyond?
I believe most of the DOW's jewels came out of the Duke's money,but whether this was his money as POW and then King,or his private fortune we will never now know.
Not only that,but as this seller bought them at the famous Geneva sale of the DOW's jewels,just how do we propose to take the money off of him?(Given that he is not a UK citizen)
If you want to argue that the money should have come back to the UK,then something should have been done when they were sold from the Duchess' estate in 1987,to make a fuss now is surely shutting the stable door after the horse has gone.