According to one source on the internet, this was what followed the great fog:
As a result, British European Airways (BEA) the state airline - each autumn would station some ground-handling equipment and staff at Southend from the end of September until early March. This avoided the need to bring staff down to Southend should an aircraft divert, thereby reducing delays because of the two-hour drive from London Airport. In turn, BEA staff could handle other airlines so diverted, such as Lufthansa, KLM and Air France, who had nominated Southend as their number one diversion. It should be remembered that, at this time, Stansted was a remote, charter-only airfield, Luton was a grass airstrip and Gatwick had a poor weather record. Passengers landing at Southend could be in Central London within one hour.