Youth provisions for IB and ESA

I have been unable to work or due to sickness and disability since 1992 when I was 19. Because I was at university at that time, I did not qualify for Incapacity Benefit, only Income Support. I subsequently learnt that I could have claimed Incapacity Benefit when I was under 25, under the youth provisions in the legislation. Unfortunately, I didn't understand the rules at the times and I was told that I couldn't apply for it retrospectively.

Being on means-testing Income Support, ESA and now UC hasn't made much difference to me to date because I have lived with and been cared for by my parents. However, my father died in 2023 and my mother is 79.

My concern now is that if my mother were to give or leave me a significant sum of money, I would lose my UC because, unlike contribution based ESA, it is means tested.

I'm fairly sure that its not possible, but can anybody suggest any way that I could claim non-means tested ESA now on the basis that I was eligible for contribution based Incapacity Benefit before, even though I didn't apply for it at the time?

My parents have set up a Vulnerable Beneficiary trust for me but it is far from ideal due to all the costs and complications associated with it. (I will start another thread with questions about this.)