UK weather: Sun seekers to seaside as hot spell sees temperatures hit 25C Parts of the country enjoy warmer weather than Portugal to last to the middle of the week A morning of mists gave way to a warm summery afternoon, as parts of Britain basked in weather that was hotter than Portugal. People headed for the park and the beach as swathes of the country from Portsmouth and to Manchester were treated to temperatures that rose above 20C - reaching highs of 25C in the South East. But the low cloud and dew-soaked lawns this morning were a reminder that Sunday's equinox has ushered in the official start of autumn - and wetter, colder weather is on the way as the weekend approaches. Splashing fun: Three-year-old Penny White plays in the sea on West Wittering Beach, West Sussex as the UK basks in an extra week of sunshine Summer fun: Temperatures reached an unseasonably high 25C in some parts of Britain today as forecasters warned people to make the most of the 'Indian summer' Serene seas: A man walks his dogs at West Wittering as the warm front makes the beach a perfect place to be for people in South East England Golden days: After a foggy start to the day in Cambridge, the trees in The Backs area emerged in the autumn sunlight in spectacular red, orange and yellow hues One mountain climber was left stunned when he reached the summit of Mount Snowdon and spotted an incredible circular rainbow. Sam Clack, 33, had spent four hours scaling the highest peak in Wales when he was met by the stunning sight. He looked over the ridge to see what is known as a Brocken Spectre, a rare phenomenon caused by the sun and his own shadow. The sun behind him projected his shadow onto the mist below, creating the colourful, halo-like mane. The phenomenon takes its name from the Brocken, a peak in the Harz Mountains in Germany where it was first identified. Mr Clack, a radio journalist from Manchester, said a retired physics teacher he met at the top of the ridge had explained to him about the Brocken Spectre - 'when he'd lifted his jaw from the floor', Mr Clack said. He added: 'I have never seen one before and may never see another, it was definitely a privilege to have witnessed it.' Apparition: The Brocken Spectre was seen in the morning mists on Mount Snowdon by a climber today Phenomenon: The rare natural wonder, caused by the sun and a person's shadow, takes its name from the Brocken, a peak in the Harz Mountains in Germany where it was first identified Cloud nine: Hiker Sam Clack spent four hours climbing to the peak of Snowdon and saw the circular rainbow as he reached the ridge