Lawyers and law firms still take legal advice from other firms in some circumstances, e.g if it’s outside of their specialism or perhaps cynically, so that someone else’s professional indemnity insurance is available if they are wrongly advised!
Also GCC will most likely have had solicitors preparing the case for them. Barristers (like GCC) do the advocacy in cases, they don’t normally do all of the preparatory work of bundles, statements, the case management timetables etc.
edit to add - sorry I meant to say @SinnerBoy