I am a modular student a few months from the end of ATPL theory and
Not clear if you have already thought of securing your ATPL theory exams to be and to remain EASA approved in the first place?
There is a short thread answering to some of that, PPRuNe search option will find you more on the subject. And look for posts by Alex Whittingham.
ATPL Brexit Theory Advice
For the flight training part, there's a list of UK ATOs that appear to have secured EASA life after BREXIT.
https://www.easa.europa.eu/sites/def...ALS_200130.pdf
There are a handful of ab-initio ATOs in the list, call them up and find out if after December they can continue providing for EASA licences from british ground or if they would refer to their sister bases abroad. If that were the case you might as well look at ATOs under Competent Authorities in EASA land, i.e. overseas, directly. With FTE in Jerez you would probably be close/closest to the british training methodology and standards.
Hope this helps,