Please note the following comparisons, taken from the Internet.

Runway lengths. Southend. 1605m. current.
Southend 1799m. proposed.
London City. 1319m.
Southampton. 1723m.

With a Full Payload the following aircraft require a minimum runway length of:-

Airbus A310 1860m.
A318 *** 1355m. 109/118 passengers?
A319 1950m. 124/144 passengers?
A320 2090m. 179 passengers.

Boeing 737/300 1990m.
All other Boeing 737's require 2400m. plus.

*** They are looking to fly 100/150 passengers a time out of Southend, the A318 is the obvious choice, with a full payload the current runway length is more than adequate.
Even with a runway extension, the A319 could still not fly out of here with a full payload, nor could any of the Boeing 737 range, which also rules out Easyjet and Ryanair.
This poses the question, why extend the runway.
With the expense involved together with all the opposition to this, there is a strong case for leaving things as the are.
It doesn't make economic sense to fly an A319 or a Boeing 737 out of here with say a 65% payload, especially as the A318 is suitable for the present runway length.

Why not extend to 1800m. because that extra meter and above brings in a different set of regulations that the infrastructure at Southend and surrounding area is unsuitable to support.

The main runway here at Southend is known as 06/24 (060 & 240, degrees on the compass)

Direction of 'take off' and 'landing' is almost exclusively controlled by wind direction of 5 knots or greater, with a cross wind, the best direction is selected or it may well be optional.
Crosswinds approaching 30 knots will usually curtail the movements of smaller aircraft, the short runway 15/33 fell into disuse some 20,years ago, but it's still there!
The approximate frequency for direction of movements is 65-70% from runway 24 out over Leigh and of course 30-35% out over Rochford.
Pretty obvious to those under the flight path, but not everyone living elsewhere would necessarily be fully aquainted.