Agree with running on the road as I've done it myself, but it is extremely insolent to call volunteers and/or fellow runners jobsworth
Go and do a proper race ;)
It wasn't about it being a 'race' at all, it was about the ridiculousness of the situation in that there was no physical way I could have been on the path with the amount of people not following instructions. I'm not arsed about it as a race or for a time but it was annoying that I couldn't get my session done because the plodders can't comprehend 'stay left'.
Optimise the session. Don't use a parkrun as busy as Encliffe as it's likely you won't get all you want out of it. Go to Hillsborough, or go and do a tempo solo elsewhere (Loxley/Damflask?). It'll save you mental hassle and you'll probably get more out of it than just an irritated feeling!