Rail passengers in the east are being urged to avoid unnecessary travel as efforts continue to repair damage to the network caused by the record-breaking temperatures yesterday.
Network Rail is urging commuters planning to use the Midland Main Line between St Pancras and Sheffield, which serves Luton, Bedford and Kettering to check before travelling due to reduced service levels.
Meanwhile, Great Northern, Thameslink, East Midland Trains and West Midlands Trains warned of fewer carriages on some services, cancellations and continuing disruption.
Train speeds are being reduced to cut the likelihood of steel tracks buckling after multiple incidents on the network, including problems with overhead equipment
The weather is also causing difficulties to flights.
Numerous travellers at Stansted also reported delays and cancellations, with the airport telling one passenger on social media that air traffic control restrictions over the south-east of England prompted the problems.
The Met Office said a new record temperature for the month was set at 38.1C (100.6F) in Cambridge on Thursday afternoon, beating the previous record of 36.7C (98.1F) set at Heathrow in 2015.