Like Ken I have been using my E Rider almost daily for more than six months and getting bad reactions from the public or police is certainly not my experience. I sometimes have people saying that I have forgotten my helmet and from time to time I have had a comment that I should not be in a bike lane, but nothing aggressive. I normally ignore comments, but once or twice I have explained the position and found people to be interested rather than hostile.
Just recently I did have two motorcycle police wave me down. They were more curious than anything and it was a friendly encounter. They were quite honest that they had nothing to do while they were on duty for the Open Golf Championship so when they saw me pass silently by they wanted to investigate. They were not very familiar with the EAPC Regs, but they were happy for me to inform them and they went off very impressed with the bike.
As Ken has pointed out no motor vehicle regulations apply to electric bikes and you are certainly not required to provide a breath sample. It is difficult to imagine that any police officers could be so poorly trained as to seriously make such a suggestion. What did the police officer think he could be giving you a warning about Jan? That is really ridiculous. In addition to your complaint I think it would be worthwhile contacting your local Police and Crime Commissioner to make them aware of the inadequacy of their officers.