Now published on the Home Office website:

Deactivated firearms: Implementing Regulation (EU) 2015/2403 - Publications - GOV.UK

Pretty unpleasant - especially for full-autos. Just think what you'd have to do to something like a Lewis or a Vickers... Naturally they haven't mentioned that the requirement to re-do previous spec deacts on sale or transfer is currently unenforceable. That won't be the case forever though.
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