hc4361- what you say normally applies for savings accounts but not for these Over 65 bonds.
From the Martin Lewis site:
With normal savings accounts, you're usually able to fill in a form (known as an R85 form), which lets the bank know that you don't earn enough to pay tax, and therefore the bank is able to pay your interest gross. However, NS&I is not part of HMRC's R85 scheme, so it will pay all interest with tax already taken off.
If you're a non-taxpayer, you'll have to reclaim the extra interest from the taxman at the end of each financial year. It's not difficult to do, but it is an added hassle. For details on how to reclaim overpaid interest, see HMRC's website.