How much should I charge?

Exactly maryeliza54 it really annoys me when some people assume that because a tradesperson charges (say)£40 per hour that is what they are getting. When they have tax, National insurance, vehicle costs, vehicle insurance, vehicle tax, fuel, liability insurances and crikey knows what else........the list is endless.... to pay out, before they see a penny of it.

Seems to me that the Plummer just wants someone to get his books in order before giving them to the accountant.
Then the accountant will do what he has been trained to do.
Smurf52, from what I understand, has no qualifications in this field apart from the experience of doing the book keeping for her husband.
I'm not suggesting that you won't be good at sorting him out and preparing his accounts but, if it were me, I would be very happy with £15/ hr.
Actually I wouldn't be happy at all! I can't bear doing my paperwork never mind someone else's mess. Still if it floats your boat....

And the other thing, a lot of the overheads are fixed costs so if they have a dip in jobs, their income per hour is disproportionately less (iyswim)

It sounds as tho you are keen on this job, I agree- don't undervalued your services, but don't price yourself so high that you lose this opportunity.

Our accountant does the annual stuff, each month I reconcile everything (receipts, invoices etc) against the bank statements and put them all together in punched pockets marked with the relevant month and bung in a lever arch file.

Then when it goes to the accountant, it is fairly easy for her to go through.

Gadabout Gran: Being dyslexic doesn't mean he isn't also lazy - people can be both, without these necessarily being linked, or either one without the other. If he hasn't got an official diagnosis and support, then I suppose it comes to much the same thing from the OP's point of view: she has to make sense of a chaotic bundle of papers.

This work isn't all profit - the assistant/bookkeeper may also have to pay tax and NI, and supply materials such as a storage and work space, print cartridges, stationery etc. This needs to be factored in to the hourly rate.