Answering this question correctly falls into two main categories.
1. Insurance cover.
2. Membership of a shooting organisation.
1. As Mike states there are a number of organisations and companies who will offer insurance cover.
The wise purchaser will study the very fine print with regards to actual cover offered. The majority of policies offered, including those offered by some shooting organisations offer a "policy of last resort". This means that in the event of a claim your providers insurance company will seek to wriggle out of the claim in the event that you have some cover by way of another policy, say your home insurance. Delays and upset guaranteed.
The policy offered by BASC is a policy of first resort. They pick up the claim and run with it. I know the man at BASC who initially deals with any claims, he deals with around 60 claims per annum, mainly for damage to property.
2. We all enjoy the sport of shooting, or we wouldn't be posting on this forum.
Shooting faces many challenges to its future. Shooters need representation both in parliament and at international level.
The ability to have somewhere to shoot, something to shoot at, and something to shoot it with is not a God given right.
There are members of society who would cheerfully see all private firearms banned. Lead shot is currently under scrutiny, and is already under a partial ban.
If you value your shooting you will join an organisation with a proven track record of defending and protecting shooting at every opportunity.
Some providers provide insurance only, at a price and don't claim to do anything else.
Some organisations provide insurance, albeit as a policy of last resort, and make various claims as to their respective representation of shooters interest. My own research conducted a few years ago proved that in the main it was either non existent, regionalised, or at a very low level when compared to the main shooting organisations. In this respect one organisation stands head and shoulders above the rest by a country mile and then some.
In the end analysis you pay your money and make your choice. If you wish to shoot registered shoots you have no choice other than to join CPSA, but they are not well know for protecting the interests of shooters. I know a number of shooters who are members of two or more shooting related organisations; good on them for supporting their sport to the hilt.
For me, its BASC all the way.
Not the cheapest by far, but when was cheapest ever the best?
You can pay monthly by direct debit for the price of a couple of pints.
webber