The central London offices of the Civil Aviation Authority are expected to remain closed until at least Friday April 10.
The offices had to be evacuated last Wednesday following a major fire in a nearby service tunnel.
All staff were safely evacuated and most were transferred to its Gatwick office.
The CAA said it was ‘business as normal’ and all essential services remain available.
A CAA spokesman said he doesn’t believe the evacuation has had any impact on ATOL holders, with yesterday’s deadline for licence renewals.
The building in Kingsway houses around 300 staff.
In total, around 2,000 people in the Holburn area were forced to evacuate office buildings in the area, which also include MSC Cruises’ offices and call centre.
The cruise line lost power following the fire and urged customers and agents to use online alternatives, but its telephone lines were fully restored on Monday.
