Around 150 firefighters were called in to tackle a fire at the Law Society’s headquarters on Chancery Lane on Saturday night.
The London Fire Brigade was called at 2240 and crews from Soho, Dowgate, Euston, Islington, Lambeth, Whitechapel, Paddington, Shoreditch, Shadwell and Old Kent Road fire stations were at the scene. The fire was under control by 0948 on Sunday.
The roof of the six-storey building and a staircase from the third to the fifth floor were destroyed by the fire. Half of the third and fourth floor was also damaged.
Around 28 people left the building before the Brigade arrived and 11 people were evacuated from nearby flats as a precaution. There were no reports of any injuries.
The cause of the fire is under investigation.
Law Society chief executive Paul Tennant said: "First of all I wanted to express my gratitude to the fire service and my relief that nobody has been hurt. I also want to express my sympathy to the residents in the Chancery Lane area whom I understand may have had to evacuate their homes.
"It is too early to comment on the cause of the fire or the extent of the damage but clearly we are extremely upset that this has happened to this wonderful and historic building.
"When the fire alarm sounded on Saturday night an event had been taking place. An evacuation ensued and I'd like to praise our on-site staff and others for their calm response. We will release more information as it emerges in due course."
London Fire Brigade Assistant Commissioner Dom Ellis, who was at the scene, said: “This was a very complex fire due to the age and layout of the building.
"Firefighters worked throughout the night in very challenging and arduous conditions to prevent the fire from spreading to key areas of the historic building, while also trying to prevent water damage.
"Crews remained on scene throughout Sunday damping down and cutting away. They also carried out salvage work to minimise damage to the building.”