He and his wife were placed under guard at their £1.5m Oxfordshire home

The Mail on Sunday's exclusive pictures show him under close protection

Deemed 'credible', it required an immediate response from Scotland Yard

BBC boss Tony Hall has been placed under protection of elite bodyguards

The Director-General of the BBC is being protected by an elite squad of bodyguards after receiving a chilling death threat over the sacking of Jeremy Clarkson.

Tony Hall and his wife Cynthia have been guarded round the clock at their home since a terrifying email was sent to the BBC just hours after he took the dramatic decision to drop the controversial Top Gear star.

Last night Scotland Yard confirmed officers were investigating the 'threat to kill' made on Wednesday, after the BBC decided it was 'credible' and alerted police.

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Tony Hall, the Director General of the BBC, leaves his home escorted by security officers

Lord Hall was placed under protection immediately after the BBC received the death threat

Lord Hall leaves his Oxfordshire home as a personal protection security van remains parked outside

The Mail on Sunday has learned that the BBC's head of security put out an urgent appeal for ex-Special Forces personnel to take part in the top-secret operation to protect Lord Hall, at a cost to licence payers estimated at more than £1,000 a day.

A security source told this newspaper: 'There was a sudden urgency on Wednesday to find an eight-man security team to protect the Director-General of the BBC.

'A select group of close protection officers were approached and told that, as a direct result of the Top Gear punch-up and Jeremy Clarkson being sacked by the BBC, the DG had received a death threat.

'Some of the operation was visible, as a deterrent, while other bodyguards would have kept a very low profile.'

Closely guarded: Lord Hall arrives back at his home in with security minders standing by

Under protection: Last night Scotland Yard confirmed officers were investigating the 'threat to kill' made on Wednesday, after the BBC decided it was 'credible' and alerted police

On alert: The Director-General of the BBC is being protected by an elite squad of bodyguards

Our exclusive pictures show that within hours of the death threat being made, Lord Hall and his wife were under close guard at their £1.5 million Oxfordshire home.

At 10.30am on Thursday, two men sat in unmarked Mercedes cars parked on double yellow lines outside Lord Hall's 18th Century townhouse, occasionally mounting patrols around the nearby streets.

At 4.40pm one of the cars, a saloon, pulled up outside the front door and the driver waved to the driver of the other car, an estate.

Lady Hall emerged from their house and was escorted to the saloon and driven off, before the car returned without her.

At 9pm that evening the two men in the Mercedes cars were relieved by a team from a leading provider of security services.

A Ford Transit Connect van marked London Protection Services Ltd drew up outside the house and two black-clad men sat outside the property overnight.

Security team members keep a close eye on Lord Hall's wife Cynthia as she escorted from the property

The firm, which has 1,000 operatives from military, Special Forces and police backgrounds, charges £300 per man, per shift.

At 6am on Friday, Lady Hall came out of her front door to speak to one of the security men, who then joined her inside the house.

Lord Hall, dressed down in a green Barbour jacket, black jeans and walking boots, then emerged and drove a mud-spattered Jeep to the front door. He filled up the boot of the off-road vehicle, watched by the bodyguards, before his wife joined him and they drove off together.

It is believed they went to their second home in the West Country for the weekend after Lord Hall's most turbulent week at head of the BBC since he took over two years ago in the wake of the Jimmy Savile scandal.

The Director-General became a target after taking the final decision to axe Clarkson, the BBC's biggest star, from his £1 million-a-year role presenting the Corporation's biggest global money-spinner.

Overnight shift: The guards remained stationed outside the property throughout the night

Two security team members hired to protect Lord Hall and his wife stand guard beside unmarked cars

He decided not to renew the 54-year-old's Top Gear contract after an internal investigation found that he had punched producer Oisin Tymon in a 30-second physical assault, following a prolonged verbal tirade. The 'fracas' was over the lack of a hot meal after a day's filming.

North Yorkshire Police are investigating – but although Mr Tymon does not want them to press charges, he has been the subject of sustained abuse from Top Gear fans who blame him for Clarkson's sacking.

One Twitter user said they hoped Mr Tymon 'visits the morgue very soon' while another wrote: 'Tony Hall BBC director, I wonder if Oisin's and your head can stop a bullet!!! just wondering.'

The chilling email was sent to the BBC just hours after Lord Hall announced Jeremy Clarkson (pictured) was being sacked

An insider said: 'With less than 12 hours' notice the close protection officers were asked if they could go to the DG's house to protect him and his family. The job was described as a "fastball", which meant that an immediate response to the threat was required. The threat was also regarded as credible.

'On that basis, requests for close protection officers to make themselves available for this job were put out on Facebook pages and groups which are strictly for approved and highly qualified security personnel. A number of close protection officers came forward and were briefed about the threat to Tony Hall.

'The security operation took various forms, including personal security at home and following his car when he was driving. '

Lord Hall has received a death threat before. In 1999 he went into hiding under police protection following a call that said he would be 'next' after the murder of Jill Dando. At the time, Lord Hall was chief executive of BBC News.

The new threat is the most serious made to a senior Corporation figure since a decade ago, when BBC 2 controller Roly Keating had to go into hiding after being accused of blasphemy for screening the Jerry Springer opera, which depicted Jesus in a nappy.

Scotland Yard said last night: 'Police in Westminster are investigating an allegation of threats to kill. The allegation was reported to police on Wednesday. Enquiries continue. No arrests have been made.'