Thanks, however I am puzzled . Somehow the code I included seems to have disappeared from my post above. So I will just try it again. It just appears to be part of S2member:
input type="checkbox" name="ws_plugin__s2member_custom_reg_field_opt_in" id="ws-plugin--s2member-custom-reg-field-opt-in" class="ws-plugin--s2member-custom-reg-field" value="1" checked="checked" tabindex="72" /
Yes, I want to receive updates via email./label
I do have Mail Chimp but I have deactivated the integration which removed what was a second check box of the same nature.
I used to have another email plugin, deactivated and deleted when I opted for Mail Chimp - could that have left something 'isolated' that does this?