This guy should shut up and get the ring out of the country while the British Museum is saying it isnt real. Once they change their mind, they own it.
The British Treasure Act says that a price has to be determined by an independent board of antiquities experts. Then the item is offered at that price to any museum. The money goes to the landowner where it was found. If no museum is willing to pay the price, the landowner gets to keep it. The serious and legitimate detectorists cut a deal with the landowner before they start looking, agreeing to a split.
It totally mistifies people like you that he is motivated by something like preserving national heritage rather than personal profit doesnt it?