I’ve heard mention of permanent interest-bearing shares but am confused as to what they are.

Pibs are shares issued by buildings societies that allow them to gain access to stock market funds without going through the complexities of a demutualisation. The shares are listed on the London Stock Exchange so prices may move daily. They are reported weekly in FT Money’s Databank section. They carry a fixed rate of interest (called a coupon) that makes them closer to a corporate bond than a share. The rates payable are currently higher than those on ordinary building society savings accounts.