I have an online business helping small UK businesses with their admin. Sometime I fill out their UK tax return for THEM to 'submit to their accountant' I tell them, few do though since they are usually very simple. I will be IAB certified before I leave to live in France.
I believe in order to do this work in France I cannot advertise myself as a book-keeper - so I just plan to keep it to 'helping with admin' (UK mostly, perhaps ex-pats in France) using my IAB certification as a reassurance for them rather than a qualification to do the work.
It is not 'illegal' to do book keeping in France, however, they do not have an equivalent profession - weird eh? If you try to explain that you're a book keeper to a French person, they can only understand it as an accountant - or at least that's how it was in Brittany when I lived there.
The French accounting system is slightly different to ours, so if you were planning on book keeping for English speakers that are running a business in France, then you will need to learn the differences and will of course have to fill out the book keeping figures on the French forms. However, if the ex-pats you're planning on helping with their admin are still in a position where they have to fill out the UK tax forms (i.e. are not 'resident' in France - do not spend more than 6 months of the year over there, or they have UK property that they rent out etc) then you'll be OK continuing to help them with their UK forms.
What I found, when I was in Brittany, was that the ex-pats that were running French businesses still like to have every day book keeping done in a UK package, so that they could understand it, but then the end of year figures had to be adjusted accordingly for the French forms.
A Bientot! Hope this helps
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Carol Saunders Lady of Ledger Book Keeping Telford, Shropshire