Just been through it - took a few days.

best way is email this address - seller-verification-enquiry@amazon.co.uk and say you are about to change legal status and here are my docs.

Give them all the docs related to company formation and some ID - Bank statement, driving licence and a recent bank statement.

Ask them what else they require.

Mine was easy as I was going from sole trader to Ltd company with no real changes. The owner was the same as was the VAT number, bank account, address, email and phone numbers. essentially just a legal status change. They contacted me around a few days after the email. They did ask for a confirmation statement from compnies house for share capital allowances. This doc no longer exists as for share capital allowances. So i got my accountant to download a similar doc from CH and sent Amazon that. It worked - i was then told to go to the transer business portal under my acccount on dashboard. Requested the transfer. All selling is suspended for around 24/48 hours - had to put my bank details back in along with charge card method and basically make sure everything in the account worked. All selling locations went to inactive so had to Uk out of holiday mode. Basically even after they tell you you are verified you need to check your account. The inventory was all still there. Its a bit of a faff but trying the process by starting the process vai the portal seems to make it slow as hell. I avoided that route.