Not content with offering a mere head cleaning tape, WHSmith sold a combined Cleaning and Demagnetising Cassette, as shown here in a Tascam Porta 05 multitracker. Contrary to some designs of head demagnetiser cassette, this one, from the 1990s, contained no circuitry. Inside it’s just a standard set of spools, plus a cylindrical magnet, around which the cleaning tape is wrapped, so that the magnet revolves in the opposite direction to the exposed tape when the cassette is run. The magnet, incidentally, is behind the red and white spoked wheel graphic. It’s not particularly strong.
As to whether this very cheap two-in-one maintenance option actually worked, it’s not easy to tell. It didn’t make things any worse (as some wacky maintenance products did), but I can’t be convinced it ever made things any better either. The cleaning tape would certainly take the residue (or some of it) off the heads on its first two or three runs, but the demagnetising was harder to evaluate. I ran a new one of these in a recorder which was quite obviously suffering from high gauss levels, and it didn’t make a scrap of audible difference after any of three runs. Maybe it did help technically, but I don’t think the effect of this sort of demagnetiser was particularly dramatic.