Interesting stuff, as we are practically in the same boat over here in the West of Germany, too! Various local authorities in NRW had created exclusion zones for petrol cars rated Euro2 and older, some of them including motorways as well. For the time being, this is off the table now, but you never know …
But back on topic for the London ULEZ. I have collected all the relevant data for our cars and the result is quite interesting:
You can see that even some of the Euro3 models (particularly the VVC models and the older TF 135s) will not comply with the 80mg/km rule. For Euro2 this can only be estimated, as there are no specific NOx emission values available. My guess would be that the Mk1 MGFs will not be able to comply, and by a considerable margin. This means taking the car to a testing station to spend hundreds only to get a negative result might not be the best of ideas.
IMHO there are just two options left to meet the stricter standards, both of which will not please you very much, Rob.
Option 1
Get a complete drive train from a Euro3 car (preferably from a 120 bhp MGF) and retrofit this to N7. This needs to be certified - the donor car’s V5 must contain the engine number and the emissions values. I know this has been recorded for TFs, not too sure about Euro3 MGFs, though.
The whole drive train including gearbox and exhaust needs to be transplanted, as emissions are calculated against distance, therefore gear ratios are important. ECU and parts of the wiring loom need to be swapped as well. Not an easy task, especially if you go for a Pektron equipped donor or even a SAIC TF, but the latter would at least give you peace of mind, as you might even get it into the Euro6 class. BUT the originality will be gone and this may cause issues when N7 would be eligible for historic vehicle registration.
Option 2
Buy a compliant F or TF whilst they’re still cheap, and mothball N7 until she’s ready to be registered as historic vehicle. On the up side, this will enable you to do some thorough restoration work on the car over the years. It might get you in trouble with Yimmy, though.