Why do you think that?
Not having a go at the cops at all, always found them quite old bike friendly, while said old bike is sitting looking pretty, however would they take original equipments limitations into consideration such as
Silencers - which would not comply with today's sound levels in particular Goldiy silencers which where not really original road equipment IIRC
Lights - six volt were ok back in the day, would your average traffic policeman know what the law is re adequate illumination on today's roads, for eg how many of the many cyclists riding at night without lights get booked.
Brakes - will they accept that in our classic case the highway code needs changed to allow us twice the amount of "thinking time"
I guess time will tell, meanwhile I intend to get mine mot'd, a fresh set of eyes is always a good thing I think, on the plus side it will be nice not to have to adhere to a certain date once a year to get it done