It depends on the officer and the situation...
If you had been in an accident you might be in a nasty situation
At worst you could be charged with using a powered vehicle without a licence - effectively driving without a licence - but you would have had to do something fairly impressive to get that sort of trouble.
If you do get any police interest just be polite and use the 'I didnt know that' approach.
Always keep the machine maintained and wear the safety gear
There is also the fact that if you are riding at reasonable speeds you can say that you could pedal the same speed as you are running.
There is always the kill switch - and frantic pedalling lol
Jemma xx