Finally made my mind up on engine, emissions?

Many moons and the odd rainy day ago i built a natty Spondon/Harris stylee streetfighter. I made a jig and made the frame so no log book so thought ummm don't fancy a q plated bike so bought a DT125 frame and logbook for a few pennies, I changed the engine size from 123cc to 598cc and sent it off....nobbers sent it back with new engine capacity as 598cc so wahey my streetfighter not only had a number plate it was classed as a classic bike...coooool or what if a little naughty.