Britain is set to bask in a 34C degree heatwave as the country braces for the hottest day of the year.

       London and the south east of England are on course to enjoy the highest temperatures on Friday, while 27 to 30C is expected across most of England and Wales. In Scotland and Northern Ireland it will be cooler.

       The sweltering peak has prompted an amber alert for "heatwave action" in the capital and east of the country.

       It comes as rail passengers have been warned to “check before you travel” with delays expected, while fire authorities say there is an increased risk of grass and open land blazes and accidental drownings.

       Health alert

       The “level three heat-health alert” from the UK Health Security Agency (UKHSA) and the Met Office, the second highest of five available, "requires social and healthcare services to target specific actions at high-risk groups".

       A level two alert remains in place for the east Midlands and south west to "ensure readiness and swift action to reduce harm from a potential heatwave".

       Health authorities urged the public to look out for signs of heat exhaustion, avoid UV rays between 11am and 3pm and drink plenty of fluids.

       Rail chaos expected

       Those relying on the railway may come unstuck, as Network Rail, which manages the country’s rail tracks and signals, warns Friday's conditions will “cause delays”, adding: “We work hard to keep you moving in hot weather. This isn’t always easy.”

       The public body said that the railway is made of 20,000 miles of steel track which can get 20 degrees hotter, expand and buckle in hot weather. Train operators have urged travellers to allow extra time for their journeys.

       Overhead lines that provide power to the trains could expand and sag, which in previous heatwaves have led to widespread chaos and cancellations.

       Network Rail said that temporary speed restrictions could be introduced on Friday to "reduce the risk of damage and keep services running but they can cause delays".

       “We have to balance the inconvenience of delays against the risk of the greater disruption that would be caused if we need to fully close the line," the body said.

       Already on Friday morning, commuters were facing rail delays, including a fault with the signalling system just outside London Waterloo station causing disruption until 2pm. Some rail operators such as Southeastern have told beach-goers to expect packed services near the coast.

       Fire risk

       Meanwhile, firefighters are warning that there is an increased risk of fires due to the heatwave.

       London Fire Brigade (LFB) said it has already attended more than 1,430 grass and open land fires across the city this year.

       This includes grassland, canal and riverbank vegetation, scrubland, parks, playgrounds, crops and woodland.

       Around 350 of these were in domestic gardens and LFB said that with prolonged periods of hot weather, there is a concern these numbers will rise.

       In the last five years, the LFB have attended almost 600 fires involving barbecues, 45 of which were on private balconies. North Northamptonshire Council has even banned all barbeques in parks and woodlands on Friday.

       Residents are also warned not to risk their safety for a cooling swim. The LFB said there were nine accidental drownings in London last year, making it the joint third highest in the UK.

       Forecast: will it be a record-breaker?

       A high of 29.5C was recorded at Northolt in west London on Thursday, surpassing the 2022 high of 28.2C recorded at Kew Gardens on Wednesday.

       Highs of 26.1C (78.98F) were recorded in Cardiff, 21.4C (70.52F) was recorded in Edinburgh and 20.6C (69.08F) was recorded in Derrylin in Northern Ireland on Thursday.

       While England and Wales will bask in the heat on Friday, it will be cooler in Northern Ireland and Scotland which will both be affected by rain.

       Britain's highest recorded June UK temperature was 35.6C at Southampton Mayflower Park in June 1976 - and forecasters do not expect that high to be surpassed this week.

       The warmest day ever recorded in the UK was July 25, 2019, when the mercury hit 38.7C in Cambridge University Botanic Garden.

       Leading bookmaker Coral has cut the odds to 1-2 (from evens) on this month ending as the hottest June on record in the UK, as temperatures are set to reach as high as 34C today.

       The firm is odds-on at 4-6 for this summer to be the hottest ever in the UK, while it is 5-4 that the UK's highest ever temperature of 38.7C is broken this year.