All money made from or in France MUST be declared in France, it is illegal to register any business solely in the UK where the income comes from renting French property or sales made in France etc. The 2010 Double Taxation treaty underpins this. This applies even if payments are made in sterling and don't leave the UK. If the money is paid for the use of a physical French property i.e. gite, lake etc it is illegal not to declare that in France.
Discocarper, if the French tax authorities raid a French venue which isn't registered in France and therefore does not have a SIRET number (and they have, several) the venue will be instantly closed down and fined back taxes for every year since it opened commercially. Any angler fishing or has booked will lose their holiday and can have their tackle confiscated for participating in an illegal enterprise.... the owner if he cannot pay the back taxes will have any French property he owns confiscated and he can be given a custodial sentence of up to four years........
And don't tell me it is tosh because I know of several individuals/fisheries it has already happened to.....including a friend of mine whose house and lake was confiscated and he was given the option of prison or never coming back to France again. He chose the latter, and the case took place in Brittany.
Any anger fishing a fishery without a SIRET number or using a French company without a SIRET number is committing an offence under French law and would have no liability insurance if anything happened to them or others on the property etc. It has nothing to do whatsover with paying tax or not paying tax, it is about whether you are registered or not in France. You can still choose to evade taxes if you want, that's up to you, but if you are not registered in France in the first place that is illegal and anyone knowingly using an illegal business is also committing illegality.
By profession I am a lawyer, by the way.
If it has not got a SIRET numnber don't go....simples!