Good question. I've had a surf through the internet and discovered this from an article by Leslie Hunt in a 1967 edition of The Essex Couyntryside magazine:
Then on the morning of Christmas Eve 1958, as fog rolled across England, both Heathrow and Gatwick airports ceased accepting incoming airliners. Until this moment Southend had not been regarded as a major diversion base by the international operators, but within a short space of time more than fifty airliners, ranging from Viscounts to DC6As and Constellation 749As, were most efficiently landed and the airport was well and truly on the world aviation map.