The CTA is an agreement between Ireland, the UK, the Isle of Man and the Channel Islands. It states that the area should be a passport-free zone. Luckily, the Irish Government will admit any person that has proof of UK citizenship. What I am saying is that the CTA is a lot more flexible than Schengen, which probably suits the countries a bit more.
The Isle of Man and the Channel Islands don't inspect anything and they are technically 'independent' to some degree.
Definately. IMO it's far more suitable than any Schengen type agreement for Britain.