The Met Office, Britain's national weather forecaster, said there was a 40% chance that the record of 38.5 degrees Celsius (101.3°F), set in Kent in 2003, will be broken.
Many thousands of jobs will be lost across the country if the UK leaves the EU without a deal, Greg Clark, the business secretary, has warned.
Johnson, who officially took over from Theresa May on Wednesday and swiftly sacked most of her ministerial team, held the first meeting of his new cabinet of ministers on Thursday.
Discussions between Britain and the United States on building up their military presence in the Gulf are ongoing, Prime Minister Theresa May’s spokeswoman, Alison Donnelly, said on Friday amid tensions with Iran.
Three Iranian vessels tried to block a BP-operated tanker passing through the Strait of Hormuz but backed off when confronted by a Royal Navy warship, the UK government said on Thursday.
Britain scrambled on Monday to stem damage to its relations with Washington by finding the leaker of diplomatic cables in which the UK ambassador called US President Donald Trump “inept.”
A British record high temperature, 38.7°C (101.6 Fahrenheit), may have been reached on Thursday, provisional data from the UK Met Office showed on Friday.
Asked by the BBC what would happen if London tore up its EU membership card, Michel Barnier said: “The UK will have to face the consequences.”
The 28 EU leaders are trying to agree on who will steer the bloc over the coming years through the looming challenges of Brexit and the rise of populist parties in Europe.