No interactions present.
I am afraid I don't have any accurate measurements but I would suggest that it was greater than 1.5 cm in length and yes I believe it was final instar and looking for a pupation site.
I noticed nothing unusual about the leg arrangement there appeared to be four pairs of false-legs (ignoring anal claspers) and 3 pairs of pro-legs just behind the head.
There was a thin yellow line/band running along the lower flanks.
This suggest I am probably right with a noctuid. There is something naggingly familiar about this caterpillar but I cannot place it for you.
Lat/Lng: 50.9, -2.7
OS grid ref: ST5516