Not sure about secondary radar. Always thought the church was the main problem. From
http://en.wikipedia.org/wiki/Southend_Airport
"..The airport's ambition to restart offering passenger flights of use to the local population dovetails with Government aims outlined in the White Paper on airport development and the Thames Gateway development. A minority of the local population have objections to this. In 2002/3 a debate centered on the idea of relocating a church further away from the side of the main runway. This would enable passenger aircraft, of a size already regularly seen at the airport, to offer passenger flights to points further into Europe. Aircraft arriving empty for maintenance are not required to have the same CAA/ICAO standards as passenger carrying flights, so at present these can operate without the required CAA/ICAO requirements. However, a compromise scheme that sees the church remain where it is, has been worked out.."
On a personal note, always like going to SEN. Lot's to see and photograph and hope the plans work out.