My mother has an expired UK Passport and has been living in Australia as an Australian citizen for the last 30 plus years.  She has now been diagnosed with a form of dementia, and as her only next of kin (daughter living in UK) I am investigating bringing her back to the UK to live.  I know she has an up to date Australian passport as she visited me last summer.

My question is, it looks like her old "British passport" expired back in 1988. She was born in England.

If I travel to Australia and try to bring her back to the UK, do I bring her back on her "Australian passport".  Should she be "applying" from Australia to be allowed to come back and live in England.  I know when I applied for my visa to visit my Mum last week, I had to apply for a visa to visit which allowed me to stay for up to 3 months.  

Would my Mum have to apply to England for a Visa even if she has an expired UK passport?  I will have difficulties with her signing stuff as at the moment she would be deemed by doctors as lacking capacity. All I want is to bring my Mum home but I don't know how difficult it will be. I have tried 3 times in last week to get an answer on the Gov.UK immigration department number but nobody can give a definitive answer.