Tarshish is the Biblical name for Crete. Caphtor is the Biblical name for Cyprus. The Cypriotes were the source of a big chunk of the Bronze Age copper supply. The Egyptians referred to them as the Keftiu.
That's why I used the word speculated about Tarshish and Britain.
It is possible that Tarshish existed in multiple different locations throughout the thousands of years of biblical history.
There are several candidate locations for Tarshish I am aware of but when tin is mentioned as being associated with Tarshish, the connection is made with Britain is one possible location.
I believe copper was more widely available than tin, making the tin trade and tin regions highly coveted.