Most UK cops, even in London, definitely don't want guns.
1. If cops have guns it encourages criminals to carry them and shoot first.
2, Cops who kill innocents by mistake already very unpopular. Public trust important.
3. British cops have reputation as nice folk, helpful to children and old ladies. They like that.
Now it isn't that easy for folk to get unlicensed firearms! Feeling is. it would get easier if cops were armed - more incentive!
Mind times have changed, I doubt if, now, a 20-year old student could carry two rifles on her shoulders on the London Underground and the only reaction, other than people carefully looking away, a child saying, "Mum, look at her!" and being told, "Sh!" (Me, secretary of College Rifle Club on way to competition in about 1963, pre-IRA compaign and much pre-current violence!)