Duncan, Why would you doubt that the game is legit. It has all the printed manuals, keyboard stuff etc. If somone was going to all that trouble and to have the disk mastered / pressed and then sell it for just £7 they can't be making much from this action.
Yes the game comes up with some protection software which checks the DVD before loading the game.
As others have the same description of the DVD it sounds that every thing is in order
Now to work out how to play the game