Hadn't actually come across this before somehow but I believe it might be end of stock as it is actually listed as 89p like the the standard one at the moment but actually scans at 40p :)

As an advocate of spicy food, I did enjoy the flavour of this.

One would assume national as there were batches of them at the time and no longer listed on their website.

https://www.frenchs.com/products/mustard/classic-yellow-spicy/