Video report by ITV News Correspondent Paul Davies
An issue with air traffic control resulted in travel chaos for thousands of holidaymakers, with a family of 62 being forced to cancel their whole trip due to flight cancellations.
The huge family holiday had been planned for eight months but after a long frustrating day at Heathrow Airport, the adults were forced to break the bad news to the excited children they would not be travelling to Rome.
"We were excited, but our hopes were shattered," two of the children told ITV News.
The story was much the same for hundreds of other travellers as thunderstorms across Europe, coupled with British air traffic control technical problems, resulted in cancelled and delayed flights.
"This is about the worst weekend ever (for this to happen). There are going to be tens of thousands of people waking up tomorrow morning where they don't want to be because their flights have been cancelled," travel expert Simon Calder told ITV News.
Passengers at major train stations were also facing disruption after the extreme weather condition caused delays to services.
Thousands of passengers were left stranded at stations on Thursday, the hottest July day on record, as temperatures of up to 38.1C (100.6F) created havoc.
Overnight thunderstorms also grounded flights, causing knock-on delays to services on Friday.
Temperatures at Heathrow reached a record-breaking 36.9C on Thursday, followed by thunderstorms in some parts of the country.
Air traffic control company Nats said the technical issue had been fixed by the mid-afternoon.
They said: "Following the technical problem at Swanwick air traffic control centre this morning, we have now fixed the issue sufficiently to safely increase traffic flow rates and will see an improving picture through the rest of the day.
"We apologise for the inconvenience caused."
Heathrow Airport tweeted: "Due to extreme weather conditions across Europe this evening, Heathrow and other airports are experiencing delays and cancellations to flights.
"We're very sorry for the disruption and advise you to contact your airline for more information."
Gatwick Airport also confirmed that weather conditions may affect air travel.
The airport tweeted: "If you're travelling with us today do check your airline, as bad weather may cause some delays."
British Airways announced that "severe thunderstorms are causing significant delays and cancellations to our operation in and out of London".
On Friday morning, people still faced problems getting into work, with Euston, Kings Cross St Pancras, Liverpool Street and Moorgate terminals all affected.
Across other parts of the country, train companies affected by the extreme weather include Great Northern, Thameslink and East Midlands Trains.
Passengers have been advised not to travel unless the journey is essential.
Only half of Thameslink's train are in service due to the weather.
East Midlands trains between Sheffield, Nottingham and Derby are also affected.
Overhead wire failures also caused disruption between London and Watford, between Preston and Carlisle and in the Birmingham area.
People looking to travel on the Eurostar from London have also been hit by delays after an overhead cable fire at Paris Nord meant power was cut.
Eurostar is urging only "essential travel" on what would be one of its busiest days of the year so far. Repairs on the overhead line are ongoing.
Further travel chaos could be caused by thundery downpours prompted by the sweltering temperatures, with flash flooding and power cuts possible.
Speed restrictions on most commuter lines were reduced over fears steel tracks could buckle in the heat, while the conditions also led to overhead electric wires being damaged, blocking all lines between London and Luton.