I've had some more time to look at the tire to decide whether to move it or bin it.

In the end, I counted no less than 6 somewhat deep gashes in the rubber that were at least 5mm long. Therefore, I'm going to bin it/drop it off at the local shop for recycling (along with a green tire that has no flat protection that I also almost wore through).

So, it seems that it stopped a bunch a cuts already and it's time had come ... I still think the roads in the UK are brutal!