It's generally not something that is done with British coins, the only grading services are based in America, and to be perfectly honest I don't like the idea of getting a coin officially graded and sealed in a holder. And I think it would be expensive (and risky) to send your coins to America to be sealed in. Different people have different opinions, so post a picture of the coin here in order to gauge an average opinion, or take it to show coin dealers face to face, who will also give you opinions. An opinion from a good coin dealer is just as reliable as a plastic holder.