I would concur with the other comments that getting a French passport would be much simpler and cheaper than going down the spouse visa route. It also wouldn't prevent you from naturalising as a British citizen after five years' residence in the UK if you wanted to.

What's your claim to French citizenship? You say your mother is French but she hasn't been registered in your family's livret de famille - was she born in France or Australia?

Am I right in saying that although not required to live in the UK, wouldn't getting an EU residence permit make claiming ILR easier after 5 years?

Yes, I would recommend applying for an EEA registration certificate as soon as the OP arrives. After five years she can apply for her EEA permanent residence card which then can be used as proof of residency to simplify the process of naturalisation.

I may be wrong and clutching at straws but my mother is a French born Australian. So she can get citizenship. I have seen another case online where someone in another country had the same situation as me and got a passport (I am half French afterall) as the French recognise blood. Or something. I'd have to find out the process they undertook but it seemed confusing. I'm holding little hope.

You need to be clearer. Is your mother a French citizen or merely born in France? Did she emigrate to Australia as a child with her French parents, as an adult or was she born in France to Australian parents?

Born in Australia to French parents and her mum claims she did the citizenship process but I'm not so sure. She definitely could apply though afaik.

Okay, so not French-born, but Australian by birth and French by descent. Providing your mother was registered with the French authorities after she was born then you can also register as a French citizen.

If she wasn't is it too late for her now?

What route do I take to start this process. You've been so helpful

I can't say it's a specialist area of mine but no I don't think so. I suspect she would need be registered before you could be though. I would approach the French Consulate-General in Sydney for more information.

Nationalité - La France en Australie

I asked my Grandma and she said she registered her with the French embassy and mum was added into her French passport.

Thanks!