UK weather: Britain basks in glorious spring weekend (even though it's still a bit chilly) London Marathon kicked off under a cloudless sky in the capital It was a chilly start across the country despite bright conditions Frost overnight in some places with a low of -2.7C in Charlwood, Surrey Met Office forecasters predicting 'mixed bag' of weather in coming week London Marathon runners were pounding the pavements under bright sunshine and cloudless skies today, but forecasters have warned the crisp spring conditions will soon 'go downhill'. A band of rain making its way eastwards across the UK throughout the day is expected to see runners towards the back of the field crossing the finish line under showers. The glorious sunshine also belied the chilly temperatures this morning, as the Met Office predicted the mercury will struggle to hit 20C in an 'unsettled' week to come. Slowly but surely: Oshia Pota, 28, soaks up the spring sunshine as she sits among the daffodils in London's Hyde Park today Met Office forecaster Michael Lawrence said the marathon kicked off in pleasant conditions but added: 'We've got a band of rain over Wales making slow progress eastwards throughout the day.' 'Spots of rain' were likely to reach London by late afternoon, he said. The UK enjoyed a 'pleasant' spring day yesterday with highs of 15.9C recorded in both Loftus, North Yorkshire, and Hawarden in Flintshire, Wales. Blue skies: It was a chilly start to the day across much of the UK, but the bright, crisp conditions were ideal for runners taking part in the London Marathon Unsettled: Dog walkers in Essex enjoyed the spring sunshine at the beach - but wore coats to keep off the chill Temperatures in the capital could creep to the same level by late afternoon today, but Britons hoping the rays of sunshine herald the start of balmier temperatures are likely to be disappointed. May is almost upon us, but there were still patches of frost in parts of the UK overnight, with a low of -2.7C in Charlwood, Surrey. While there will be some sunny spells across the UK in the coming week, Britons are advised to keep their umbrellas and jackets close to hand along with their sunglasses. Sunny start: Runners basked in bright sunshine as the London Marathon kicked off in the capital this morning, but temperatures remained chilly early on Bright: The sun shone brightly over London as the men's wheelchair elite approached the finish line during today's marathon Making the most of it: Kite-flyers didn't let the moderate temperatures put them off making the most of the sunshine over Martello Bay beach in Clacton-on-Sea Calm seas: Lifeguards took part in a practice session in a sunny Chalkwell, Essex, today Mr Lawrence described bands of rain moving in from the Atlantic, bringing wind and showers to the UK. This week on the whole is on the unsettled side and quite changeable. 'We've got bands of rain moving in from the Atlantic, although it won't be a wash out.' Preparing for spring: Fallow deer at Longleat Safari Park in Wiltshire were shedding their winter coats - and birds were spotted plucking the moulting fur to line their nests Cheeky: Jackdaws were spotted plucking at fallow deer shedding their winter coats at a safari park in Wiltshire 'Mixed bag': Met Office forecasters are predicting a week of changeable weather 'A fair bit of cloud' is also expected throughout the week, he said, with conditions likely to change from sunny to grey even 'within each day'. 'Temperatures in the south might manage 20C in the South East later in the week, perhaps by Thursday,' said the forecaster, who added that current temperatures were fairly typical for the time of year. So it will be warm at times in the south. 'Broadly speaking we've got a north-south split, with the north wetter and windier, but still with some sunshine. In the south it will be less wet and windy. While temperatures dropped to 2.7C in Surrey overnight, Lossiemouth in Scotland recorded a low of 7.6C, in a 'flip' of the typical pattern of warmer conditions in the south.