Model IDs are unique codes that refer to a specific make and model.
They bear no relation to manufacturer model codes, they're just
codes that can uniquely identify a specific model sold in the UK
(imagine them as a barcode for vehicle models).
For most cases, one model name has a single code associated with it.
However, models can sometimes be listed against multiple model codes
(eg: BMW M3).
There are no rules for how these codes are allocated or chosen,
so in some cases a single code may span multiple model generations,
and in other cases a single model generation may have multiple codes
(which could correspond to facelift models, or different body styles).
Note: the years listed against the model IDs are my 'best guess' at
the year that production for each individual model started.
Unfortunately there's no definitive source that lists the correct years.
I've added these codes so you can make the most of the data that's
been released by the DfT. However, it's not always clear which models
or generations the different codes refer to, so you may have to do
some more research to understand them properly!