Some classes of vehicle ownership, or use, are "Crown Exempt" from the requirement to be covered under the Act including vehicles owned or operated by certain councils and local authorities, national park authorities, education authorities, police authorities, fire authorities, health service bodies, the security services and vehicles used to or from Shipping Salvage purposes. Although exempt from the requirement to insure, this provides no immunity against claims being made against them, so an otherwise Crown Exempt authority may choose to insure conventionally, preferring to incur the known expense of insurance premiums rather than accept the open-ended exposure of effectively, self-insuring under Crown Exemption.
Yes, you surely can avail the NCB if you change your insurance provider at the time of renewing the policy. All you would need to do is producing a proof of the earned NCB from your current insurance provider. You can produce the original copy of your expiring policy and a certification that you haven’t filed any claim for the (expiring) insurance plan. A renewal notice or a letter stating that you’re entitled to the NCB from your previous insurance provider can be a proof for this.
Comprehensive insurance covers all of the above and damage to the vehicle caused by the driver themselves, as well as vandalism and other risks. This is usually the most expensive type of insurance. It is custom in the UK for insurance customers to refer to their Comprehensive Insurance as "Fully Comprehensive" or popularly, "Fully Comp". This is a tautology as the word 'Comprehensive' means full.
Car insurance will prove a benefit if you ever experience a wreck, vehicle theft or other unpreventable problem on the road. The policy can help pay for such concerns as your own vehicle damage, injuries and related costs. Coverage can also pay for the damage you cause others if you are deemed at-fault in a wreck. With your policy, you can reduce your chances of significant financial losses after an unfortunate accident.
But liability coverage levels come in threes — you’ll probably see something like 50/100/50 up to 250/500/250 in typical policies. You can think of these limits like: individual injuries / total injuries / property damage. Insurers are a little more technical, calling them bodily injury liability, total bodily injury liability and physical damage liability.