Investigations are ongoing into the cause of a large blaze that gutted a £2.8million mansion in Hampstead Garden Suburb in the early hours of Sunday.

More than 40 firefighters in eight fire engines were called to the property, in The Bishop’s Avenue, just before 5am, when smoke was seen billowing from the roof.

Three adults escaped the six-bedroom house, which is owned by Iouri and Natalia Chliaifchtein and sits on one of London’s most exclusive roads, dubbed ‘Millionaires Row’.

The Russian couple were the victims of a £2.1million burglary at the house in 2006.

A gang, led by then 23-year-old traveller Gerrard O’Leary, broke into the mansion, stealing £1.7million in cash and Cartier jewellery and taking two £400,000 sports cars from the driveway.

O’Leary was later jailed for seven years for that and other burglary offences.

Neighbours described the couple as reclusive and said a team of private security guards patrolled the property.

A London Fire Brigade spokeswoman said 70 per cent of the first floor was damaged in Sunday’s fire, while the roof was completely destroyed. The property’s large staircase was also damaged.

One woman was treated for shock at the scene but no-one was injured.

Crews from Finchley, Barnet, Willesden, Hornsey, West Hampstead, Wembley and Edmonton managed to get the fire under control by 7.12am but the flames were not fully extinguished for another couple of hours.

Fire investigators continued work at the house yesterday, though the LFB reiterated this morning that it is still not known if the fire was started deliberately.