A couple of notes on the RTHK website suggest that the building was initially named 'Electra House', then later changed its name to 'Mercury House':
[The Lucky Dip show had to be moved from] RTHK's Concert Hall on the 6th floor of Mercury / Electra House to the City Hall Theatre across the road. More...
1950. [RTHK] moved to Electra House as headquarters. More...
Comments
Electra House
A couple of notes on the RTHK website suggest that the building was initially named 'Electra House', then later changed its name to 'Mercury House':
Re: Electra House
Electra House was completed in 1950.
Source: http://www.info.gov.hk/isd/40th/2.html
The name change to Mercury House came later.