In the UK, you are not allowed to keep what you find. You must inform the government, and then the government buys it from you at a price that they determine.
“...the government buys it from you at a price that they determine.”
...so at about 10% value would be my guess. Then they tax the sh** out of that.
I actually don’t find this objectionable. A find like this - with such historical value - should belong to England, not to an individual who happened upon it. How do you even put a price on it? It should go to a museum, not an auction house where it will end up in the private collection of some Russian oligarch.
Unless you are a Biden.