Council registered does not equal reputable. It means they breed commercially for profit, and meet minimum welfare standards.
You're right regarding price too, the puppy is one of a litter of 6 and the last remaining available so clearly people are willing to spend £2k
Do you know for definite it’s the last one? How? Reputable breeders usually have a wait list and all puppies are spoken for before birth. “The last one” or “someone dropped out so we have one unexpectedly available” are red flags.
However the endorsements not to breed etc are a good sign. My pup was endorsed- i had to neuter and not breed, because he was bred to show but didn’t meet breed standard as he was too small, but with the fashion for “teacups” chances were someone would have given it a shot- and indeed I was asked several times in the street in he was available for stud..
£2k is a lot and could be good or bad. Could be they’re pricing because they’ve had lots of vet care etc, and to weed out timewaster, or simply they’re driven for profit. I’ve only really come across that sort of price for trendy portmanteau crosses. But bichons are one of the desirable breeds at the moment.
The only thing you can do is keep asking questions. Contact vets who did the checks, google show results, pedigree, everything you can think of.