Cobra neck 1 year post-op. What went wrong? (photo)

You comment that you went to THE pre-eminent neck lift surgeon in the UK. This begs the question of did you have a facelift as well. It appears you did not, and whatever your initial concern was, it is clear that you now need to go the THE pre-eminent face and necklift surgeon in the UK.
This just means that you need to have a more comprehensive approach to your problem with a lower facelift, re-opening the neck, repair of the platysma, modification of the submandibular glands, and redistribution of the neck and lower face skin. You may also need some fat grafting in the neck, centrally.
Any approach limited to the neck, is going to fail, as it certainly did despite the excellent reputation of your surgeon.

first, a correction is possible. There are different fat compartments of the neck, that need to be addressed during surgery. Not only the compartment under the chin. There is also an excess of skin notable. A real neck lift will help your situation and will achieve a nicely contoured neck. Neck lifts can be quiet complex, requiring work on some muscles and sometimes the glands. Short cuts rarely work. Diligence, an aesthetic sense, knowledge and experience are key. I hope this helps.

You probably needed more than just a neck lift to correct the excess skin. I would suggest doing a full facelift lift or add the mini lift so that the skin can be repositioned and pulled back tightly.