I've not read through all the posts so I'm not sure exactly what's required but the beauty of the Halfords system is that the stuff they mix on site, or you order & arrives in-store the following day if it's certain colours like yellow, is the traditional cellulose base & not two pack.
I'd never even consider using 2k paint unless you had the appropriate equipment, air fed mask, etc. etc.
Most trade paint counters nowadays only seem to sell 2k paint with very little cellulose available. I'm not sure why the H & S police haven't stopped Halfords selling cellulose yet, I'm sure it's only a matter of time ☹️, but when I spoke to them last year they had no plans to stop supplying it.
Hope this helps
Mark.