Why is this allowed to happen?
Anne
Because they are scum who think they can get away with taking the piss. Unfortunately, the fact they are still trying it, suggests the UK public are mostly pretty thick individuals that fall for it.
Fortunately, you are a more enlightened type, who can get a few quotes from other "piss-takers", of which some will be cheaper (perhaps significantly) than your previous premium, and certainly cheaper than your renewal, at which point you will have the pleasure of suggesting something unmentionable to your current insurer. And lo, suddenly their price drops (it being christmas and all that, and they have targets to meet, and other sob stories), to the point it makes it easier & cheaper to stay where you are (because you don't have to prove security, alarms, NCB etc to the new insurer).
And then you have the pleasure of deciding whether to stay, or stick with the unmentionable suggestion and go elsewhere. Its a win-win, don't let them fuck you over.