The Egyptians also used cocaine in the mummification process. Either they had contact with South America or they mummified so many people that they used up every tobacco & coca plant in the Middle East.

The land masses between Britain and somewhere like Egypt were populated and (axe) trade over a few hundred miles in the Neolithic is quite well documented. The Britons may not have had direct, face to face contact with the likes of the Egyptians, but indirect trade is a probability.