It depends on the type and series.
Go online and do a search for a government bond calculator. You enter the series identifiers and the bond serial number and it will answer all of your questions. And it tells you what the bond is worth, what the interest rate is/was and if it's still accumulating interest.
Any nationwide bank can cash it in for you if that is what you choose to do.
Mike and Tina
Beachcomber 1995 Sea Ray 550 Sedan Bridge