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Your id popped up while I was uploading mine! I have added my agreement to your Geometrid ID but am not sure about Swallow-tailed moth. Porter indicates that it should have a small dorsal protuberance just forward of the first pro-leg. I can't see it in the photo but possibly it is hidden because of the angle the photo is taken from.
I'm far from sure of that specific ID, which is why I also added a more certain more generic ID.
I've added an example of a confirmed Swallow-tailed moth caterpillar at http://www.ispot.org.uk/node/130190
I think we will need to original observer to provide more details of the caterpillar to safely get this one to species level.
Lat/Lng: 53.8, -1.6
OS grid ref: SE3139