Derived from the phrase "Dim as a Toc H lamp." ("Dim" meaning unintelligent - see dim.)
Toc H is a Christian Service club created in 1915 during the First World War. Each Branch or unit of Toc H may be issued with a lamp which can be used for the traditional "ceremony of light" at meetings. The small wick gives off a dim light. (Source: Wikipedia).
Definitions include: We will have to work out how much we owe each other, won't we? Thull 'e tu be (There will have to be) a recknin (a calculation or discussion) not it? (won't there?) This is in Nottinghamshire dialect and 'not it' is used for isn't it, don't we, aren't they, do you agree, wasn't it, weren't they, didn't he / she /it, won't you, won't they