The government Affinity scheme is as you suggest a scheme that gives a discount on new cars to certain organisations suchas blue light workers. However searching through sections and sub sections on the government website, would be like finding a needle in a haystack.
I would imagine if a dealer has the will, they can work around it, by not inclluding the Affinity discount rather offering a discount for no part x etc, jst as any customer can. As you say walking into a dealership at the end of the month.
The MG4 is a cracking car know MGhave sorted the few niggles. Anyway good luck with your search and do let us know what you choose 🙂