>>> Is there a central register where folk with allergies can get all recall details ?
Th Trading Standards website carries the information but you need to click on the links to read the full details. (However you can choose to view up to 100 entries per page, saving you from having to click through lots of pages):
https://www.tradingstandards.uk/consumers/product-recalls-and-safety-notices
The information is duplicated on the website of the Food Standards Agency, where you can read the full details of each entry straight away (without needing to click on a link) but where you need to work through several pages if you want to go back to look for older entries:
https://www.food.gov.uk/news-alerts/search/alerts
(I prefer the latter format myself).
>>> Is liability then removed?
Lawyers could argue about that for years! For a company to be successfully sued the person taking action against them would need to show that they had been negligent and/or that they had failed to display due diligence.
As an analogy, if you slip on a spillage in a supermarket which has only just occurred (leaving the staff no time to identify and remedy the problem), resulting in injury, it's unlikely that you could successfully sue the supermarket for damages, as there was no negligence involved on their part. However if the CCTV showed that the spillage had occurred quite some time before, and had been totally ignored by staff members who must have clearly seen it, then a claim for damages would almost certainly be successful, as a court would rule that the store had been negligent in failing to clear up the spillage.
So, in the case of a civil action for damages resulting from a mis-labelled product, a court would have to decide (based upon the 'balance of probabilities') whether or not the complainant had successfully shown that the store had been negligent. The test in a criminal case (of 'proof beyond all doubt') is far higher and the CPS (or other relevant agency, such as the FSA) would only commence proceedings where there was extremely clear evidence against the relevant company (or one of its staff).