The irony of the Great British Summer

The Great British Summer is what Marks & Spencer calls its range seasonal food this year. Some of it is really delicious. That said, it is not seasonal, as it does not look much like summer and it does not feel like it. it often rains, it is mostly cloudy and it is not warm. Whatever I said recently in another post, it seems that summertime is not quite here, or already gone. I have heard the expression great British summer before, but I have no idea where it is from. Or what inspired it. Because right now, it is supremely ironic.