What stopped BBC 2 from broadcasting on its intended launch date of April 20, 1964?

BBC 2 was scheduled to be launched on April 20,1964. Only 25 minutes before airtime, however, a fire at Battersea Power Station caused a power failure in much of London, including the BBC Television Centre.

Instead, the channel launched with a short news bulletin, read by reporter Gerald Priestland, from the BBC's news studios in Alexandra Palace. This was followed by an evening of instrumental music from contemporary West End musicals and "BBC 2 WILL START SHORTLY" captions occasionally interrupted by "MAJOR POWER FAILURE" captions accompanied by apologetic announcements explaining why people weren't able to watch Cole Porter's 'Kiss Me Kate' or fireworks from Southend Pier.

BBC 2's first scheduled program was in fact Playschool, broadcasting the following morning. A second "launch" program, which featured the now famous scene of presenter Denis Tuohy blowing out a candle in the darkened studio was shown as part of the news bulletin later in the evening, which is just as well as it's now folklore that someone had forgotten to put hands on the studio clock for the intended first night!