I am from Essex, and there are 5 sites i know about or played in the essex area. These sites are as follows
Skirmish Airsoft Billericay - outwood common farm, Billericay Essex
Airsoft Plantation - 40 acre plantation, goatsmoor lane, stock
Dragons Lair - The secret nuclear bunker, Kelvedon
AWA Herts - Matthams Wood, Sawbridgeworth
Raw - Paintball Extreme, Pillcox lane, Tendering.
As i dont know where you are in essex, I can't say how long it will get to them for you. But with me being in southend. I can get to all these sites with in an hour max.