It may seem a trivial matter, but the bond between a person and their toast topper is a powerful one. For decades, Marmite jars were sealed with a sturdy, reliable metal screw-top lid. But in 1984, in a move towards modernisation, the manufacturers switched to a plastic lid.

The public reaction was, to put it mildly, not favourable. An "outcry" from devoted fans lamented the change, viewing it as a betrayal of tradition. It was a classic case of "if it ain't broke, don't fix it."

While the plastic lid ultimately remained, the passionate response highlighted just how deeply ingrained Marmite is in the British psyche. It is more than a food; it is a cultural artefact where even the smallest detail, like the material of its lid, is a matter of national importance.

Source: http://www.marmitemuseum.co.uk/history.html