The 11-year old Swiss Cottage building was originally designed by Bennetts and received an RIBA Award in 2003.
The latest works respond to rising visitor and audience numbers. Circulation routes have been improved by measures including relocating a staircase and moving the box office and entrance doors.
Meanwhile the theatre's daytime appeal has been boosted by the inclusion of rosewood veneer panels, which provide warmth and a luxurious feel against the existing concrete and steel interior.
My photos of the project were featured in the Architects' Journal.