I think the correct answer will be that Marks and Spencers don’t make a polypropylene tie.
It is Viz after all.
I do believe you have answered your own question, as I very much doubt you would be able to find any manufacturer in the world making ties from such an unsuitable material as:
polypropylene = propylene ploy.
Marks and Spencer = send a crank sperm
However, if 'crank' was in fact Ranck, the very same guy who discovered head direction cells in the rat dorsal presubiculum, a structure that lies near the hippocampus on the dorsocaudal brain surface, then call me a Stupendous Yappi.