Figo wrote: how relevant is it to a magician?
Most corporates and large gigs will require you to have it. Anything could happen which you could be sued for - burns from flash paper etc., latex allergies from balloons, any injury or damage to a spectator or their belongings (you accidentally step on their foot, breaking their toe, they trip over on the way to the stage, you knock their drink over their designer clothes, lose their ring etc. etc.)
It will make you look more professional and cover every possible eventuality. The UK is becoming more of a litigation culture.
Better to be safe than sorry !