Ok...
If you want insurance to cover you in case your bike is stolen, if you have household contents insurance, it may already be covered. But you need to check the small print as regards detail. There will be a limit on the value of bike, type of lock and where the bike is locked. It is fairly standard for conditions to specify a type of lock and that the bike must be locked to an 'immoveable object'. This is normal.
You may choose to get your bike insured separately, but again - it is normal for value of bike, type of lock and where/how it is locked to be detailed.
As with all insurances - if you do not adhere to the terms of the insurance, the policy can be deemed to be invalid, so any claim you make can be refused quite legitimately.
If you are referring to insurance such as public liability where you are covered in the event of an 'accident' which is your fault, you need to join a cycling organisation such as British Cycling (you don't need to race or intend to race to join) or the CTC: Cyclists' Touring Club (you don't need to be a cycling tourist to join). Included in membership (everyday cycling, silver or gold for BC) you will get up to £10m public liability insurance plus legal help, and also legal advice & support in the event you need to make a claim against someone else in an 'accident'
Indeed I highly recommend joining a cycling organisation - the membership benefits are worth it if you end up in some sort of incident. My husband was knocked off his bicycle in a hit-and-run, injured and bike damaged, yet he was still able to claim compensation thanks to the above as he had a solicitor helping him every inch of the way and taking the stress away from him. It's one of those things you hope not to have to use but if you do you are very, very glad you have the benefits.