There is nothing wrong with haggling in UK or any place. At the end of the day they know their margins all they can do is say no.
Over the last couple of years I decided it was time for both myself and SWMBO to have a nice watch each, I check all online best deals then go to my favourite local in UK jewelers shop and ask them how much they can better it by. I bought my Omega at more than 20% off ticket price and last year bought SWMBO a very nice watch with same discount. Both times there were others in the shop happy to bebuying at ticket price for some reason.
They know me very well at the jewelers now, not as the bollshy guy who demands the cheapest price, but as a repeat customer who spends money in their shop not in a competitors shop. All I do is get as close to their acceptable margin as possible, nothing wrong with that in my book. We even get tea and biscuits served whilst we are there.