How much of it is being held up by immigration issues and other legal stuff? I know the Scots were pretty ticked after the Brexit vote and could get really screwed over by Brexit.
How much of it is being held up by immigration issues
Marginal, like almost nothing.
other legal stuff
This is a big part of the problem. Laws that have been enacted under the EU era, have not been in effect under "UK law". This means a lot of "rewriting" or reformulating and this comes with a lot of different viewpoints from a lot of different politicians.
The Scots are very pro EU and do feel fucked due to Whiskey exports to the EU and their decision to remain in UK. The main problem interior however is the Ireland/N-Ireland issue, both Ireland and N-I do not want a return of an active border between the areas. There is a lot to say for this standpoint and the issue is especially relevant since Theresa May's conservatives have no majority in parliament (She lost her "snap elections" last year) but need the backing by the Northern-Irish conservatives DUP. Whom will never agree to anything other then an open Irish border and could topple the cabinet which would mean new elections.
Add the total mayhem within parliament and May's conservative party itself whom have not been able to agree on just about anything since "brexit". All in all the whole process lacks vision, a plan and planning. Which is no surprise since everyone connected to "the leave camp" jumped away when they got their vote instead of actually leading. All this and more even before the EU is involved or even presented with a plan.......
All in all its a magnificent clusterfuck, the UK has been in political crisis for almost 2 years and its the best reality TV this side of the Ocean I tellz you!
Well:
Japan was never in EU
The British themselves cant even agree on a deal
3, This is about more then just trade deals