To help in keeping this thread on track, this is what I believe to be the current situation. I'm happy to be corrected by those with better knowledge.
It is important to realise that there are TWO pieces of legislation that affect deacs and they are getting muddled up with each other.
The first is the implementation of Commission Regulation 2015/2403 on the guidelines for deactivating firearms. As this is a regulation it is automatically implemented by EU countries and was adopted by the UK on 8 April 2016. This makes it illegal to sell or otherwise transfer a deac unless it conforms to the 2015/2403 regulations. It does NOT ban military deacs.
The second, and more worrying piece of legislation is the proposed set of changes to the EU Firearms Directive 91/477/EEC. Amongst other things, this would ban military deacs, even if deactivated to the 2015/2403 regulations. An EU committee, chaired by Vicky Ford MEP, has consulted with a large range of groups that would be affected by the changes and come up with a set of revised proposals. These revisions include removal of the clause to ban deactivated military weapons and also a clause that says deacs do not need to conform to the 2015/2403 regulations if they conform to an existing national standard that can be shown to be equivalent. Should this revision be adopted, deacs to the latest UK specification would probably comply, earlier deacs with full moving parts probably would not.
However, there has been considerable push-back against Vicky Ford's revisions from a number of countries including, I understand, the UK. The proposals are due to be debated by the EU in June, so they are not UK (or anyone else's) law yet.
I hope that helps!
Andy