And, in addition to all of the above, should you stop and ask anyone, (older than about 45 years, I would think!), you could also ask for directions to the "Beehive" as it is the white round building behind Belgrano that has been there many, many years and uses the same or very adjacent parking space.
To first find Gatwick, from the Midlands,(M1?), find the M25, turn Eastbound ,(anti-clockwise), then exit to the M23 and then all as Lou Scannon said.