Hi
Hope this helps.
Fenlands Gun club in Orsett, 10 to 15 minutes from upminster. Shoot alternate Sundays, nice basic shoot, 50 birds, memberships are available. Its behind the pub (Dog and Partridge) in a farmers field. Next shoot sunday 11th.
They have a facebook page
You could also try ETL in Tilbury, linford.
Probably old threads on both here somewhere