The butter mountain that vanished

The price of butter in mid‐1970 was hardly higher than it had been ten years earlier. Now, a year later, butter is much more expensive. Our main supplier, New Zealand, has raised its price to us by about 60 per cent, to £507 a ton for packet butter. The price of butter from Denmark, our second most important supplier, has gone up at the wholesale level from £388 a ton to £558 a ton. Why has the price of this commodity, which people had almost come to believe would remain fixed in price for ever, suddenly make such a great leap forward?