Network Rail is preparing for widespread rail disruption as thunderstorms sweep across parts of the UK. Rail tracks are expected to flood after drought hardened the surrounding ground, rail bosses said, which prevents heavy rain from soaking into the soil. Therefore, when heavy rainfall hits, water could run off the parched ground and overflow the railway tracks, therefore disrupting services. The warning comes a week after a train carrying 150 passengers derailed in extreme heat near Lewes, East Sussex, leaving 30 people injured.The Met Office issued thunderstorm warnings on Thursday for parts of the UK over the coming days and into the following week, with some Brits having already experienced heavy rainfall.It will be the first time much of Britain, left bone dry from months of soaring temperatures, has seen rainfall in weeks.Meanwhile, nearly three quarters of England and all of Wales are in drought due to a record-breaking summer of heatwaves – with 10.1 million people affected by hosepipe bans.Rainfall totals for July ranged from 26 per cent of the typical average for northwest England to as little as 1 per cent in the southeast. Two people were seriously injured when a train derailed near Lewes, East Sussex Investigators are looking into whether the tracks had expanded in the heat and started to warpExperts have, however, warned the return of rainfall may not be enough to reverse the drought conditions affecting much of the country, with weeks of above average rainfall needed to make significant changes. Speed restrictions or service suspensions are imposed on train services when floodwater rises above rails.Network Rail told the Daily Mail they 'are not predicting major disruption from flooding in the short or longer term this year', but said they are 'not complacent'. The warning comes amid heightened scrutiny of Britain's railway safety following two derailments in the space of 24 hours last week. Three people were injured in an incident in Lewes, East Sussex, on August 13, while there were no casualties when a train came off the tracks but remained upright south of Wickford railway station in Essex.The eight-carriage Southern service came off the tracks between Haywards Heath and Lewes at around 3.54pm on Thursday, with three carriages overturning and passengers forced to scramble out of the wreckage as temperatures climbed above 35C (95F). Pictures from the scene show passengers standing on top of the overturned carriages, with emergency crews including Sussex Police, British Transport Police, paramedics and East Sussex Fire and Rescue Service rushing to help those inside. Action taken by Network Rail to mitigate the risks of flooding include deploying inflatable barriers, clearing debris from drainage systems and building water pumping stations at hotspots.Leading academics warned of disruption from flooding despite attempts to tackle the issue.