Right well I've taken a few photos next to a foot long ruler, so the size, depth, and location of the pothole is unmistakeable. I didn't bring the usb cable with me to work so you'll have to wait until I can get them off tonight to see.
As for my flat tyre event, I was wondering, is it possible the tyre managed to stay airtight after the pothole, but then opened up during the hardish left turn at the roundabout, as the sidewalls began to stretch and tuck under?