I'm going to be absolutely blunt about this. I believe the industry is corrupt and needs strict regulation. Apart from some of the ridiculous questions they ask (what the hell does your job, if it doesn't involve using the car, or your marital status got to do with insuring your car?), there is absolutely no reason or excuse for one insurance quote to be double (and often much more) that of a similar quote. It's blatant profiteering based on nothing but the hope that people will find it too much hassle obtaining multiple quotes.
I wouldn't mind so much but you're effectively paying for a piece of paper anyway. Nothing physically happens unless you have an accident, nobody has actually done anything except printed out a document and posted it to you. And most of the time they encourage you to do it online so they don't even have to do that. You're just subsidising those who do have accidents.
I was recently charged a £20 admin fee when I had to update my insurance details because I changed my car. Why? I completed all the details online and nobody at Hastings had to do anything at all, so why am I being charged for completing my own form? The whole industry is just one giant scam in my opinion.