Green monster

Bit of a gardening marathon today. Looks like the weather is about to turn for the worst so we both got stucvk in and blitzed the mowing, strimming, weeding and general gardening stuff. While Caroline was digging she came across this huge green catepillar/slug thing with white and black diagonal stripes. The front end is bottom right and it's got a spike (tail) at the rear. The picture is about life-sized, 6–7 cm long. A very odd beast, identification comments welcome.

|   5:25:17 PM