Fullers is very good on tap - provided you find it at the right place.
Here in the States, you have to find a place that pays attention to how they maintain their beer and how quickly they turn over inventory. A good 'British or Irish style pub' in a metropolitan area will probably be best. If you can't find that, give it a try in bottles. But again, the same sort of axiom applies. Find a beer store that does a high volume.