I found two caterpillars struggling to cross the path on the way to the lottie yesterday. One was about two inches long very fluffy yellow with some flashes of red along the body..The other was absolutely HUGE..about three inches long and very, very fat. A dull greeny buff colour but with this rhinocerous like horn at the head end. I collected both on a stick and placed on a near by tree. The yellow one came quietly but the horned beasty reared up and attacked the stick. So please what are they? Have a feeling that they must be moth caterpillars rather than butterflies.
Have a look at http://www.whatsthiscaterpillar.co.uk/ - hopefully you should be able to find them there.
Thank you Juliet; The yellow fuzzy one is a Sycamore Moth and the other huge one is a Poplar Hawkmoth.
This site is awesome! Some scary looking caterpillars out there.