You can use Geoff Sullivans CWGC website to serach for Civilian casualties bewteen 10/12/1940-11/12/1940
http://www.hut-six.co.uk/cgi-bin/search39-47.php
There are 230 Civilian deaths on those two dates, and they are registered or listed in the following districts/areas
Birmingham County Borough (CB)
Acton Municiple Borough (MB)
Cheltenham MD
Bexhill MB
Newhaven Urban District (UD)
Greenwich MB
Westminister City
Fareham UD
Wembley MB
St. Marylebone MB
Hornchurch UD
and the list goes on, this is a sample of the first 4 pages of casualties out of 12 from the site. You may find a district where Southend and Westcliff on Sea is located or near.