At the moment carers are only eligible for home responsibilities protection from 1978 if the person for whom they were caring was receiving certain benefits. There is no credit for those who cared for disabled people who received severe disablement allowance, HNCIP or a retirement pension.
You may be interested in these active petitions
The current situation is unfair and illogical. All carers should receive national insurance credits for the years where they cared for someone so that they are not penalised for giving up work in those circumstances.