At approximately 6pm this evening the sky turned a purple-black from the south west. Lightening was flashing across the sky in "chains". The main cloud was moving south to north but clouds appeared from the west (very black like wisps of smoke). They started rotating into the main cloud mass and appeared to be swallowed up by it. There were some rumbles of thunder but nothing earth-shattering and then the whole cloud mass which was right overhead appeared to suddenly rotate - there was a terrible downdraft (the wind screeched) - it picked up a 10ft tree in the garden and put it back down 6" to the left of where it started - didn't actually uproot it, took the cover off the flat roof of the shed. Leaves and twigs swirled off the trees, flowers blew everywhere, there was torrential rain .............. and after about 10-20 seconds it was all over! The clouds seemed to lighten almost immediately and by 6.15 the sun was shining. Was really scared for a moment as I thought it was a tornado - must have been pretty close to one! Does anyone know what this was? I've heard of "rotating scud" - if that's the right term.