The DWP used to issue letters stating you were on income-related benefits but seem loathed to do so now. Our local hospital insists on verification being no older than 3 months for recovering travel costs so we do tend to have problems also but you can claim from the NHS Business Services Authority(?). Some years ago when I found out you could claim health costs, by providing receipts and a good case, I was able to reclaim several hundred pounds that we had paid out for various things. I think it is worth trying as I did not think we would be successful but surprisingly were.
