Boris Johnson was at Chequers over the weekend where he hosted friends for a party.
Cabinet Office minister Kit Malthouse, who will chair another emergency meeting on Monday, claimed it was unfair to criticise the Prime Minister and insisted Mr Johnson had been fully briefed on the situation.
Downing Street insisted it was “not unusual” for Cabinet ministers to lead such meetings, as the Prime Minister was at his country retreat Chequers over the weekend where he hosted a party for friends.
Mr Johnson was also defended for taking a test flight in a Typhoon fighter jet on Thursday as the first of the Cobra meetings on the weather emergency took place, with No 10 arguing it is “important that he has a detailed understanding of the working capabilities of the RAF”.
Shadow levelling up secretary Lisa Nandy said: “We think the Government ought to do a number of things: first is to turn up to work.”
She told Sky News the Prime Minister has “clearly clocked off”, adding: “And so have many of his ministers in his Government.”
Ms Nandy argued there should be a dedicated Cabinet Office minister to co-ordinate an emergency response and she urged Whitehall to work with local areas to ensure resilience plans are in place to end the current “patchwork” approach.
Temperatures are set to soar into the high 30s in some areas on Monday, while Tuesday is predicted to be even hotter, with temperatures possibly reaching 40C (104F).
The UK is facing travel disruption, closed schools and health warnings, as the Met Office issued its first red extreme heat warning covering both days for large parts of England.
Mr Johnson has described taking off in a Typhoon from RAF Coningsby in Lincolnshire like a “vertical firecracker” on Thursday before he took over the joystick to perform various rolls and a loop-the-loop.
The Prime Minister’s official spokesman argued that Mr Johnson, who is set to leave office in September, has a role in directing the RAF in worst-case scenarios, “so it is important he is aware of some of these capabilities they have”.
Asked if he needs first-hand experience to understand this, the spokesman said: “It’s important that he has a detailed understanding of the working capabilities of the RAF.”
Allies said the gathering at Chequers was a “private informal event” and no taxpayers’ money was spent on it.
Chancellor of the Duchy of Lancaster Mr Malthouse said it was a “very unfair criticism” to attack Mr Johnson for not attending the Cobra meetings.
The Cabinet Office minister told LBC Radio: “It’s literally my job to chair Cobra. The Civil Contingencies Secretariat sits in my department.”
He said Mr Johnson “appoints secretaries of state to do this kind of work and that’s what I’ve been doing”.
Mr Johnson’s spokesman added: “It is not unusual in Cabinet Government for Cabinet ministers to chair these sorts of things.”