Someone recently explained to be that copyright cannot be sold, only the exploitation rights can. Even if they are exclusive and indefinite.
Is this the case, or can you still copyright?
The UK government says "If you decide to sell or transfer your copyright there would need to be a written, signed contract stating a transfer has taken place. This is known as an assignment". Which implies that you can sell your copyright. What cannot be transferred is moral rights, though they can be waived (so, you can waiver your right to be called the author, but you cannot transfer that right to someone else).