IT'S black, strong, rich and, if you use too much, very, very sickly. We fed it to the Curmudgeonlets, it was fed to us, to our parents and, no doubt, to our grandparents too.

Whether you hate it, or love it, it is a unique British institution that has stood the test of time. And, to my great delight, they are not going to change it. For the manufacturers of Marmite have decided to stand steadfast in the face of fashion.

Marmite, the coal-black yeast extract, is celebrating its 100th birthday. And, joy of joys, its distinctive yellow label has never been changed. Nor will it be - despite pressure from the trendies in the marketing business.

Now these are people who make a great deal of money by re-branding and re-launching products which are dear to many a British heart. They charge many thousands of pounds for this service and claim that this leads to increased sales and profits. But does it?

I mean, have you spent more of stamps since the post office became Consignia? I doubt it, cos the good old Royal Mail seems to be on the verge of going bust and is struggling like mad to rid itself of the irksome duty - laid down by charter - that it must deliver mail to any address in the UK.

That means every hilltop farm in the Dales - and even remoter spots in the Hebrides - which is, of course, expensive. Consignia would rather just deliver in towns, which is cheap.

Whatever happened to that stirring slogan, The Mail Must Get Through?

British Steel wasn't doing too badly, either, until it became Corus (or is it Chorus - I really can't remember?). This is an extremely daft name - what possible connection does it have with steel? - and the company has been laying off workers ever since.

The trouble, I suspect, is that the new brand of Armani suited businessmen now getting to the top of industry have got to do something to prove just how switched on they are. Even it means driving the business to the edge of bankruptcy.

Apart from the fact that a well-tailored Savile Row outfit makes Armani look like a boiler suit, this also illustrates a state of mind: change for change's sake. If it's old, throw it out - even if its old and works. This, of course, also applies to people in this ageist age.

It was the American air force in World War 11 that introduced the phrase, If it works, don't fix it. And the Americans haven't done too badly, despite their present problems.

Faced with their centenary year, the Marmite people were said to be besieged by the marketing men to tart up the brand to give it a "younger image."

Well, when the female Curmudgeonlet was doing the compulsory back-packing tour of the world a couple of years back, she would stay in the same place just long enough for us to send her - air mail at huge cost - huge jars of ...Marmite.

You don't get much trendier than a bright young graduate waiting in a doss house in Nepal until her prized parcel arrived. It's called brand loyalty. Change it at your peril.

* The Curmudgeon is a satirical column based on a fictitious character in a mythical village.