Annual?
Do you have a link for that? Most VAT returns like mine are quarterly.
Annual returns are for businesses of under 1.3M turnover and AFAIK you still make payments on account through the year, targeted i guess for small businesses that do not reclaim a lot and have little change in monthly cashflow patterns.
Currently i work for an EU based company and invoice EU reverse charge VAT. I have no clue how this will work post March 2019 and currently it seems nobody else does either.