why are you wasting your time? there's no way this can be safely connected up. Unless the same model cooker is fitted in the uk and you can get uk NG injectors. Even the french mains gas is different to ours so a standard conversion won't be available. You'll also need the instructions in English, this a legal requirement.
SFAIK, the gas is the same natural gas G20 or propane G31. If you can get the correct jets from the manufacturer for the propane to NG conversion, I don't anticipate a problem. The manuals may be available on-line.
no its not. its a different composition, very slightly anyway, probably wouldn't realistically make any difference but manufacturers can't say its been tested so not allowed. we have the same gas as spain and portugal though asfaik. Everything else is ifs and buts. I will put money on this thing going in the skip or back to france.