Obviously, if your pup/dog hasn't been treated during any period of insurance then there is no risk when you change - but if they have had anything other than routine treatment (even if you haven't claimed on the policy) - think very carefully before changing the policy - it may have implications in years to come 
Paddy is ready to be picked up at noon today, so I'll let you know how he is when he's back and being cuddled!
Rachel's hit the nail on the head, more succinctly than my original post. If you're pup doesn't have anything happen/arise during that six week free insurance period, then you're safe to pick whichever policy you want going forward, because you won't be going into the new policy with anything which the new insurer can reasonably say is a "pre-existing condition" which is excluded from pretty much every policy I've seen. It's really a counsel of caution for those who are still in that six week period who have had something happen (e.g. Dood with Poppy) or those who are getting ready to pick up their puppies soon. For the former category - check with your vet whether any issues your dog's been treated for are capable of recurring - and would it be "recurring" - like colitis flaring up, rather than repeat bad luck - like your pup broke its front pay during its first week with you and then its back leg at six months old - this wouldn't be a "recurrence" of a "pre-existing condition". for those who are just about to get their puppies - if you can afford it, just ignore the six weeks' free insurance and get your preferred policy in place from day one, just in case.
Edited to say - I can't criticise M&S - I still think it's a great policy with fantastic levels of cover and I'd highly recommend it. It gives whole of life cover, the vet fees are set at the highest lever (£7k per annum I think). Pretty much EVERY policy will exclude "pre-existing conditions" - the point is that if something which amounts to a "pre-existing condition" arises in those first six weeks of free insurance cover from the Kennel Club's provider, then you should seriously consider staying with that insurer - it's good cover, not quite as good as M&S and a bit more expensive. But the price difference is nothing when you consider that, after the £500 I'll be handing over today, we have spent more than £950 on treating Paddy's colitis so far (not yet seven months old) and that if he goes onto steroids etc, this will mean that we have a lifetime of uninsured costs. We're lucky in that we can afford that without it causing us to hurt financially, but it would be much nicer if an insurance company were paying! For anyone with a healthy puppy still within the first six weeks' free cover, I'd suggest getting the M&S cover straight away - just in case!
Denise
