I'm from Brentwood but haven't lived there for years (although the routes are still the same, I suspect).
Riding around Stock, Ingatestone, Blackmore, Writtle, Chelmsford, Great Baddow, the Hanningfields etc. (go into google maps and make a loop for yourself) always used to make for enjoyable cycling back in the day. Not too hilly (yeah, I know, Essex is flat) but the countryside should be lovely this time of year, although I don't know about the state of the roads or the quality, or lack of, of driving there now.