Louise Haigh signed off on a nationwide emergency wildfire alert that startled millions of people across the country. 

Ms Haigh, who is head of the Cabinet Office, is understood to have approved the alert, which led to panicked Britons jamming 999 lines and startled drivers swerving across motorways.

Sirens blared out unexpectedly on millions of mobile phones across the country at 7pm on Friday, warning the public against lighting anything that could cause a wildfire, such as barbecues, firepits and fireworks.

It was the most extensive use of the UK's emergency alert system to date. 

The Conservatives, who devised the system more than a decade ago, said the alert was only intended to be used in cases where there was an imminent, direct and mainly localised threat to life.

A Cabinet Office report explicitly warned against its use for 'lower level' incidents for fear of creating a 'cry wolf' effect, in which phone users either disabled or ignored the alert in cases of genuine emergency.  

In a press release published shortly before the alert, Ms Haigh said: 'In response to the continued risk posed by wildfires, the Government has taken the decision to issue an Emergency Alert to England and Wales.

'This is the most extensive use of the UK's Emergency Alert system in response to an active incident, and reflects the seriousness with which the Government is acting to safeguard people and property.'  

The Government had initially considered sending a targeted alert to the areas which were most affected or at risk of wildfires.

However, by the afternoon, Ms Haigh's department decided to release the alert across the country following calls from the Fire and Rescue Service, The Telegraph reported. 

But the plea from fire chiefs soon came back to haunt them as emergency switchboards became overloaded by members of the public accusing their neighbours of having a barbecue.

A spokesman for Hampshire Fire and Rescue Service said: 'Whilst it's reassuring to see that people are taking yesterday's emergency alert about disposable BBQs seriously, we'd ask that you only call 999 if there is an immediate risk to life or property, for example if fire is spreading or is uncontrolled.' 

Frustrated cinema-goers and broadcasters added to the complaints about the disruption, while there was confusion across Wales after the alert was sent out in Welsh – despite only a quarter of the country speaking it. 

Some residents received the message four times – twice in Welsh and twice in English. 

Domestic abuse charities also expressed concerns about the unplanned alerts, as it could have risked exposing secret phones used by victims.

The alert also caused chaos to live television shows, including The One Show's 20th anniversary special.

Hosts Alex Jones and Roman Kemp were left stunned as alerts began to ring throughout the studio.

Jones, 49, who clearly did not know the alarm would be issued, said: 'You couldn't make that up could you. 

'I think that's the fire alarm...I'm doing my best to keep a straight face. But we continue,' while her co-host Roman Kemp, 33, looked equally as confused. 

The alarms also disrupted hosts on Sky Sports News and the BBC Proms on Radio 3.

One unlikely benefit of the disruptive alerts was that dozens of prisoners had their hidden mobile phones seized after the loud noises blared out from inside their cells on Friday evening. 

Phones were seized from inmates in Frankland in County Durham as well as at Feltham and Belmarsh in London.

An insider told The Sun on Sunday: 'Governors are laughing about it because so many have been caught with phones after the alert. It took prisoners by surprise and loads of their phones went off really loudly in cells and other areas.

'Loads were caught red-handed and it also provided loads of intelligence about where phones were.

'Prisoners can't really get rid of them and, when there were more staff on, officers started spinning cells to find ones that had gone off.' 

The Prime Minister appointed the convicted fraudster to her powerful role, as well as Chancellor of the Duchy of Lancaster, after she masterminded his victory in the Makerfield by-election in June. 

Her position in the higher echelon of Mr Burnham's administration comes less than two years after she was forced to resign from former PM Keir Starmer's Cabinet.

This followed the revelation that she had been convicted of fraud during her twenties, with Ms Haigh quitting after just four months as transport secretary under Sir Keir.

She admitted to misleading police after wrongly telling officers her work phone had been stolen when she had been 'mugged while on a night out' in 2013 – before later finding it at home.

According to the Cabinet Office report on mobile alerts, drawn up by the Coalition Government in 2014, the system was devised for cases such as chemical spills and bomb explosions, or extreme weather events where there was an immediate and direct risk to life.

The report said: 'Responders agreed that the system would lose its impact if it was used too regularly... It should not be used too frequently and only for the most serious of emergencies, or recipients may become complacent.'

It also expressed concern about 'the potential impact of miscommunication through distorted information and lack of action due to miscommunication, for example a "cry wolf" scenario'.

Mr Burnham said on Friday: 'This evening, an emergency alert has been sent to people across England and Wales as the wildfire risk remains very high.

'The request came directly from fire and rescue services... During this period of extreme heat, I'm asking everyone to take extra care.

'Please do not light any fires in gardens, the countryside or other open spaces, including parks, moorland and wooded areas.'

A Conservative source told the Daily Mail yesterday: 'It was designed for terrorist attacks, not to tell people how to cook their sausages.' 

One woman swerved across three lanes while an elderly man pulled over onto the hard shoulder near Chorley, she said.

Ashkan Kalashy was driving on a single carriageway in west Wales with his two sisters and nephew when the alert went off as he was making a sharp turn.

'I almost lost control of the car,' he told The Mail on Sunday. 'If I wasn't more careful I might have crashed.

'Three phones were going off at different times – and during the first time in unison. It sounded like Armageddon was happening.'

Stephen Pollard, a former editor of the Jewish Chronicle, who was driving when the alert sounded, said: 'I wasn't able to pull over and so wasn't able to see what was causing a noise so loud it made me nearly crash with the shock.

'What a ludicrous use of the national alert system.'

Edmund King, president of the AA, said that motorists should only look at messages if they have found a 'safe and legal place to pull over'.

Former Treasury adviser James Gillespie, who was watching a horror film in a cinema in central London when a wave of the alerts went off, said: 'I don't think there is any good reason to be sending repeated alerts about wildfires to every iPhone in Central London.

'I've lived until recently in California where they have regular natural hazards and I've never experienced anything like this where it is so repetitive.

'If the aim was to devalue the system and encourage people to opt out of emergency alerts, this was absolutely the way to do it.'

Farcically, just hours after the alert sounded, a huge fireworks display was held at Wembley Stadium during a performance by Canadian singer The Weeknd.

The stadium said the display was a 'controlled performance' and a team of fire safety experts was on site for every event.