Wow! I think you shouldn't have been taxed on the AA. How do you pay income tax? Do you do a self-assessment or get an accountant to do it for you?
In either case, AFAIK Attendance Allowance should not be included as part of your taxable income. Like interest on an ISA account, it should be disregarded. I guess you'd have to put it in the assessment somewhere - it's been years since I did one - but it should be under something like "non-taxable income".
It might be worth seeing if you can relaim the tax back.
I believe that in tax years where you did not do a tax assessment and paid too much tax, you can just inform the Revenue. If they agree, they will repay it, up to five years back.
If you paid too much tax in a year when you did an assessment, then you have to claim what is called "error or mistake relief", and I think this can also go five years back.
By "five years" they mean five years after 31 January following the year for which you're making the claim.
It could really be worth it if it made the difference between being a non-tax payer and tax payer, if it's only the AA that's pushing you over the tax-free personal allowance. In which case you could receive things like interest on saving account gross as well...and you could get rebates on those too...
The Revenue would investigate your claim, and probably look at ALL your tax affairs to make sure you were entitled. But they are pretty good at doing tax rebates.
It sounds as though you need to go through the calculations with your tax accountant.
Are you getting something like Carer Allowance? Now that *is* taxable...