At large one uses the genuki site to find out which registry office was the overseer for an area.....
so we have "Tollesbury, in Essex" .... by entering Tollesbury Essex genuki into google should bring an answer > but in this case it doesnt but we know its part of the historic port of Maldon , so one googles Maldon genuki >
which brings u to this link
http://www.ukbmd.org.uk/genuki/reg/ess.htmlon the genuki site one will find Paul Langstons PDF "Regindex" and in that will have this
Maldon ESS 1934 1972 Maldon before 1934 see Maldon All Saints;
Maldon St. Mary; Maldon St. Peter;
Goldhanger; Heybridge; Great Totham;
Langford; Littl eTotham; Mundon; Steeple;
Tolleshunt Major
Maldon ESS 1972 1974 Chelmsford
Maldon All Saints ESS 1837 1934 Maldon after 1934 see Maldon
Maldon St. Mary ESS 1837 1934 Maldon after 1934 see Maldon
Maldon St. Peter ESS 1837 1934 Maldon after 1934 see Maldon
so now when u go to the freebmduk index , essentially to get certificate references of your ancestors or kin for Tollesbury u have the option of searching under
Maldon or Chelmsford as the registration offices at the period specificied by the regindex or genuki notes.
Similiarly if you go to family search one may find a parish record under Tollesbury but the microfilm scope may be under Maldon or Chelmsford
and in this case
the film scope is >
Tollesbury Parish Registers
BAPTISMS 1817-1837
but one checks Hugh Wallis list on ancestry for the actual films and their scopes, which can also be done on the family search . org site (LDS) for you to order in to your local LDS viewing library....
which indicates a County Archives Office or Facility has the original parish records if they survived the ravages of time....
here is the link to paul langstons regindex>
http://www.ukbmd.org.uk/genuki/Reg/districts/index.htmlothers may be able to contribute on this topic but I have explained the mechanics as best as I know how....

marty