Ensign have registered a new route, the X81H, which will run on Saturday 2nd December only, giving Shenfield and Brentwood a more frequent than usual direct bus to Lakeside and Grays. Timetable here.
Also on 2nd December, running that day only, is Ensign route X21 between Ongar and Upminster via Brentwood. It'll be every half hour on that day. Timetable here.
Both routes will run half-hourly throughout the day.