How accurate are they? Even when I go out think I’ll try to push it, I’m never in the anaerobic zone and rarely in the threshold. Given that I can feel the lactic acid in my legs I must be anaerobic occasionally?

They’re adjustable aren’t they?

HR zones anywhere are only as accurate as you’ve calibrated them to be.

Nickc yeah they are adjustable, I’ve not done a max hr test yet so need to do that really.

Odds on getting a max HR are minimal. Your better of basing them off your threshold HR.
http://home.trainingpeaks.com/blog/article/joe-friel-s-quick-guide-to-setting-zones

Works well enough for me after I inputted my max HR, which I worked out by checking from a couple of XC races.

Also rarely get in anaerobic unless I’m deliberately riding intervals of a decent length.

I did find that as I got fitter I was slowly drifting downwards in terms of actual effort – despite riding hills at same pace.