A second train derailed on Friday – hours after rail bosses insisted the lines were safe in hot weather.The Greater Anglia service crashed off the tracks in Essex less than 24 hours after a Southern Rail train's carriages flipped over in Sussex.There were no reported injuries in Wickford on Friday and pictures showed the train remained upright, with just the front coach derailed.But it has sparked fears record-breaking temperatures are causing the tracks to buckle following the crash in Lewes on Thursday afternoon.Two passengers were taken to major trauma centres with 'severe' injuries following that derailment.Another 18 were treated in hospital after three carriages flipped on their side.Lewes MP James MacCleary revealed he had raised concerns with rail bosses days earlier over the line getting 'bumpier' due to the heat.It has also emerged a safety inspection took place on the section of track where the train derailed just 24 hours before the crash. A Greater Anglia train from London Liverpool Street to Southend Victoria derailed near Wickford station in Essex on Friday The train remained upright after coming off the tracks as Britain sweltered in its fifth heatwave this year Police, ambulance and fire crews are all present at the scene where the train, carrying around 40 to 45 passengers, derailed British tracks are designed for average summer temperatures of 27C (80F), but they have been topping 37C (99F) in parts of the South-East this week.John Whitehurst, chief executive of Greater Thameslink Railway, reassured travellers that derailment is 'incredibly rare' and 'the railway is safe' in hot weather.He told Radio 4's Today programme: 'We have control processes in place that involve inspection, temporary speed restrictions or even suspending services if that's required.'But hours later, the second train came off the tracks just south of Wickford station at 2.12pm.Air ambulances scrambled and stretchers were seen on standby as police and firefighters were also dispatched.There were around 45 people on board the service from Southend to London Liverpool Street.Footage from on board showed smoke billowing outside the windows.Aaron Poyser, who lives next to the railway line, was in the garden when he heard an 'almighty crunching sound'.He told the BBC: 'It's almost like someone was shovelling stones. I saw this plume of dust and smoke. You could see the train had come off the tracks. It was quite scary.'Rail staff, police and members of the Rail Accident Investigation Bureau were seen inspecting the tracks yesterday with investigations to establish the cause under way.Martin Frobisher, a director at Network Rail, said: 'We would ask people to avoid speculating on the cause of any incidents until further information is available.'He said investigations 'will look at all possible causes and factors' as he admitted the hot weather has 'presented exceptional challenges to the railway'.The derailment adds to growing fears that Britain's infrastructure cannot deal with the heat.Mr MacCleary told Times Radio: 'I had a meeting last week with GTR [Greater Thameslink Railway], who are the parent company of Southern Rail, and we did discuss the track and the fact that it has been a bit bumpier in recent months, which is possibly a result of the incredibly hot weather we've had recently.'He said he cannot 'speculate' but added 'rail companies have been reporting that the extreme dry conditions have been affecting embankments and track conditions'.He added: 'We've had a lot of speed restrictions in the area recently, which is directly related to the heat... there have been concerns about the condition of the track recently, definitely.'On Thursday, a temperature of 38.1C (100.6F) was recorded at Kew Gardens in west London, making it officially the hottest day of the year. Another train derailed in Lewes, East Sussex, on Thursday and the carriages flipped on to their sides