A number of TV channels went off air on Saturday evening following a fire alarm at a broadcast centre.
Viewers of Channel 4 reported seeing a still screen for about 25 minutes, while Channel 5 was also off air for about 30 minutes.
Welsh broadcaster S4C, another affected channel, said the BBC, ITV Paramount and E Music were affected as well.
Red Bee Media blamed an "activation of the fire suppression systems" at its broadcast centre in west London.
Channel 4 confirmed two of its channels, Channel 4 and More 4, were temporarily off air in a tweet, though service has now resumed.
A spokesperson later said: "We did come off air due to technical issues and steps were taken to put this right as soon as possible."
Red Bee Media, which handles playout services - broadcasting technology - for a number of channels, said: "As a result of this incident and the automatic safety measures set in motion at the time, several services originating from the broadcast centre have been disrupted."
Staff were evacuated safely, the spokesperson added, with people allowed to return to the building after firefighters said it was safe.
"We are continuing to work to restore all services and remedy any issues caused by this incident," the spokesperson added.
"To avoid speculation, we will not make any further statements until all services have been fully restored and we have concluded a full investigation of the cause."
A spokesman for S4C, the Welsh language public service TV broadcaster, said: "As a result of a fire alarm at a television distribution centre in London on Saturday night, S4C's transmissions were lost on the Freeview platform for most of the evening.
"S4C's broadcasts on Sky, Freesat, Virgin Media, S4C Clic or BBC iPlayer were not affected.
"Other channels affected included BBC, ITV, C4, C5, Paramount and E Music.
"S4C apologises to all those who failed to see their favourite programmes on Saturday evening."
Channel 5 went off air for some viewers at 19:00 GMT, with a message on the channel saying: "We apologise for the interruption. We'll be back with you as soon as we can."