Do I need to register as an auto-entrepreneur business here in France?

I have been house sitting, without payment, in France since August 2011 with a couple of two or three week breaks when I returned to the UK, where I have a shared residence with a family member (not a partner). I no longer own or have a tenancy agreement for a property in the UK, but consider myself a UK resident for income tax purposes.

My earnings for this period have been less than £1000 and have come entirely from my UK web businesses and affiliate websites selling to US and UK customers. I have just set up a new website design and online marketing service for gite owners, who may be resident in France or the UK.

I am undecided how long I will continue to take on house sitting assignments, but would like to know if it is necessary or advisable for me to register as an auto-entrepreneur. I have looked into advertising on AngloInfo, for example, and they have asked for a business SIRET number. I am just starting to actively promote myself and want to make sure I’m properly and legally prepared for when I land some enquiries.

I anticipate most, but not all of the work I do, will be done over the internet rather than face to face. The business will operate exactly the same way when I’m resident in the UK again as while I’m temporarily resident in France. Clients may be resident in the UK or France and have businesses registered in the UK or France.