MOTORISTS and walkers on Dartmoor stopped to watch the relatively rare sight of a twister on Sunday afternoon. The twister ? a funnel cloud caused by a strong wind, which can cause substantial damage ? was spotted in the Yelverton and Princetown area in late afternoon. Heather Stanley from Princetown was part of a group from the High Moorland WI on a coach returning from a visit to Rosemoor Gardens. She said they spotted the twister at about 4.40pm and watched it for about ten minutes, until if faded. ?I think it must have been the tail end of it. When we were going across the top of Merrivale the sky was black and we could see it, but by the time we got to the prison quarry it seemed to have changed, and it had a long white tail coming down through the clouds,? she said. Police and rescue services received no calls about the mini tornado, which was not believed to have caused any damage to property. The American meteorologist Dr Ted Fujita discovered in 1973 that the UK has the highest frequency of reported tornadoes per unit area in the world. The Meteorological Office estimates that there are 30 to 50 tornados in the UK each year, but they are short-lived and often pass unnoticed across uninhabited countryside.