When I did it in 2013 there were two Gfa starts. Either the green start with the celeberaties or a special section at the front of the red start. Think the cut off for the red start may have been a previous time of 3.10?
If you are running in October in Worthing best to just wear a vest and shorts (commando). Make sure they are both wicking. Anything more and you will boil. The cooler you are the faster you will run. Rub yourself over with Vaseline to avoid chaffing.
Dress as if were 10 degrees C hotter than it really is is the standard advice.