There ARE two runways at LGW and it IS the world's busiest single runway operation...
Gatwick does have two runways.
26L / 08R and 26R / 08L
The second runway is used only when the main runway is unavailable. The runways are much too close to be used at the same time and there are some stands on Pier One that musn't be used when the secondary runway is in operation.
http://www.ead.eurocontrol.int/eadba...2010-11-18.pdf