An engine mil light on (malfunction indicator) is not at present an mot fail .Neither is an airbag warning light.The only light that has to work correctly is an Abs brake warning light.This situation will change in the very near future ,but as yet nothing is confirmed.hth

I thought the change took place 1st January just gone - and that advisories would be issued until March 31st (tomorrow) after which it'll be a fail.

Or did I misunderstand the announcement?

Try googling (other web search engines may be available) new MOT requirements or something similar.

It would appear you're in the clear, however if it's indicating an engine management problem your emissions may be outside limits.