I take it you mean the one on corner adjacent to headlamp - From memory of my mark 1 the plastic cover has a small tab at the bottom that sits into a clip, you can use a screw driver to prise it up and then pull forward and out. From memory on my mark 2 they are included within the glass headlamp and not separate.
Glad you had a good one Richard. and nice to see you've gave the car a good thrashing too. one day i'll make the trip to St. James's Gate myself.
having spoken to some Irish friends the Guinness is better over there.
although at my local one of the five bar staff takes the time to make a leaf on the head. ok it tastes the same but makes it special