For all practical considerations you are defenseless.
No, we aren’t.
Yes, most UK’ers wont defend with guns they don’t own. But the UK has a fairly high proportion of people with knives, swords. Many of us collectors.
Even if I wasn’t a gun owner, I would still have a .50 air rifle, several .177/.22 air pistols, NINE proper samurai swords, many knives (commando, flick etc), a baseball bat , a WW2 German bayonet. Not to mention kitchen knives and anything else nice and heavy and handy. Oh and my fists, lol.
Some very realistic replica guns as well: PPK, Colt 45, Automag, 44 Magnum. Even take away any sort of gun and I can defend myself.
Ok, so I am more ‘tooled up’ than the average Brit, but most UK men will have some knives and replica samurai swords knocking about. Over and above cricket/baseball bats, kitchen knives and handy blunt tools.
I get the point you make, about UK lack of guns. So most Brits may not be able to stop someone at 100/200 yards as you can en masse, but neither are we quite as helpless as you fear/think.