BA said in a statement that thunderstorms had caused significant disruption to their flight schedule in and out of London.
Passengers hoping to travel from Northamptonshire railway stations over the weekend are being warned that disruption caused by the heatwave will continue over the weekend.
It follows major disruptions at the airports yesterday, after thunderstorms stopped flights being able to take off. The rail network, which was crippled in the heat, struggled for a second day, and Eurostar passengers were advised not to travel.
This afternoon, Gatwick Airport tweeted: "Flights to and from Gatwick and other London airports are subject to delays and cancellations, due to a technical issue with Air Traffic Control".
Rail passengers in Yorkshire and Lincolnshire are being warned to expect another day of delays and cancellations on the trains, with people intending to travel further afield being asked not to travel if they don't have to.
Gatwick, Heathrow and Stansted were among the airports who blamed extreme weather for delays and cancellations.
The company has said services on the London St Pancras route are subject to an amended timetable due to overhead line issues in the West Hampstead area.
West Midlands Railway said overnight work to fix damage had caused delays and many trains started the day out of place, resulting in cancellations and shorter trains.
Another image shows a collapsed man being treated by medical staff outside the train.
Apologising to commuters for delays and cancellations, Phil James, from Network Rail, said: "The extreme temperatures made travelling by train very difficult at times and we thank passengers for their patience while we worked hard to get people moving again".
Although much cooler weather swept across the country on Friday, thunderstorms caused fresh difficulties for air passengers.
Temperatures reached up to 38.1C (100.6F) in parts of the United Kingdom on Thursday, however the weather is expected to keep within the mid-20s to the low 30s range on Friday.
"We have a technical problem with a system at the Swanwick Air Traffic Control Centre which is causing some flight restrictions".
Great Northern Rail said on their website: "We are advising customers to use alternative routes wherever possible". While train operators and Network Rail are working together to minimise disruption, we ask passengers to check before they travel and consider travelling earlier on Thursday if possible.
Along Scotland's Moray Firth coastline the temperatures will range from 25-27C, while in the south-east and East Anglia, the mercury will rise to 30-31C.
The Government's advisory Committee on Climate Change has warned the United Kingdom is not prepared for the increase in heatwaves that is expected with global warming.