Just some food for thought: Unless you are rocking around on £6,000 bikes, I would self insure.
You are effectively paying for someone to save on your behalf, insurance companies may not even pay out in every instance of loss or theft, IMO it's a rip off. Insurance is for catastrophic loss, e.g. your house burns down and you can't afford to rebuild it. Why not just save yourself, and earn a return on your savings?! I.e. You are not paying someone else to get rich and get to keep your savings (plus returns) when in the highly likely eventuality your bike is NOT stolen.
Buy a proper set of locks and, use them correctly and you will not lose your bike. Take the time to create an anchor at home where you can lock them up safely if you fear theft at home. If someone else damages your bike, you may have the option to seek compensation from them.
If you have the value of your bike in savings, and can easily afford to replace it at any time. There is no need to insure. If you can't afford to replace the bike, you are spending too much on it in the first place!
Note: Third party liability on the other hand, is extremely important in case you hurt or injure someone else as serious injuries can cost you millions (catastrophic loss).
If you're the type of person who insures a bike, you are probably not very wealthy, now ask yourself, why are you not wealthy?