Odd jobs: must I declare my work?

I am British, 66 years old and live with my French partner in the Pyrénées-Orientales.
I worked in Brussels for more than 15 years, until 2006, and before that I worked in various jobs in the UK, some employed and some self-employed.
I receive a modest pension from the UK Pensions Service and another modest sum from my years working as an independent marketing consultant with a small company in Belgium. I have never worked in France.
My career was as a marketing research consultant, and from time to time I am asked to do ad hoc consulting work for one or other of my old clients and do not know exactly what my commitments to the French state should be.
Is it enough to declare the earnings on my annual UK self-assessment tax form; do I need to register for TVA; do I need to register with the Chamber of Commerce and so on?
I do not want to become a micro-enterprise and to get bogged down in bureaucracy – just to be able legally to earn a few extra euros and pay tax if I must. Can you give me guidance on the least onerous course? M.R.

IF YOUR earnings from consultancy work are unlikely to exceed e32,100 a year, you may wish to consider registering as an auto-entrepreneur.

The set-up procedure and your quarterly returns and payment can all be done online. You will pay 18.3 per cent in social charges and you can also opt to pay income tax as you go, at a rate of 2.2 per cent.

There is no VAT to pay and you do not need to register with your chamber of commerce. If you earn nothing in a quarter, you have nothing to declare or pay.

The Connexion publishes a helpguide on the auto-entrepreneur status.