misty,
I collated together some links to all (most?) things useful with respect to the IVA.
Have a look here:
http://www.haynes.co.uk/forums/showp...9&postcount=10
Annex 1 of "The Individual Vehicle Scheme - A Guide to the Approval of Light Passenger & Light Goods Vehicles" (the link is in the above link!) tellls you what N1, M1 etc. is.
Regards,