No you dont need a grey card for uk bikes like you say take your registration v5 and your insurance cert and your driving licence card.
Some years they look through them and other years they dont even bother to ask for them.
You must have working lights(front atleast) for the scrutineering though if your bike lights arent wired up then a set of bicycle lights will be fine.
If you havent been before its one of the best Trials Ive ridden this is our 6th year and cant wait 6 weeks time we shall be there!!!