They are both hawk moth caterpillars. The paler green one could be a privet hawk moth caterpillar but elephant hawk moths come in that colour as well and the brown one is an elephant hawk moth caterpillar.
Cacoethes: An irresistible urge to do something inadvisable
I've never seen a green one that pale but I notice the one of the Butterfly Conservation page is the same. The ones in my garden have really bold markings:
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
elephant hawk moth… wow!!! What a beauty!😍
We don't get them here - I have hawk moth envy every time someone posts photos
I live in west central Scotland - not where that photo is...