When the BBC launched the first high-definition television service, the threat posed by Nazi Germany was already evident, and plans for the closure of the service were laid well in advance of the declaration of war. The reason for the closedown was twofold; one, with resources at full stretch fighting the war, television for around 20,000 viewing families in London and the Home Counties was a luxury the nation could not afford; and two, the single transmitter at Alexandra Palace would serve as a direction-finder for enemy aircraft approaching London.

So on 1 September 1939 at around 12.15pm the service came to an abrupt halt. A Disney cartoon, Mickey's Gala Premiere, was the last programme shown before the transmitter was switched off.

There has been speculation on why Britain, a nation in the throes of the Depression and bracing itself for the hardships of war, should have launched a television service that few could receive, and fewer could afford. One government minister of the time, Lord Swinton, stated later that the Government only gave the go-ahead for television because it wanted to encourage the development of cathode-ray tube technology, essential to effective radar defences. Certainly the technology came in handy, as did the know-how of the engineers at Alexandra Palace, many of whom worked in radar during the war.

There was a defence role too for those engineers who remained to look after the transmitter at Alexandra Palace. It was deployed in the 'battle of the beams', in which broadcast signals were used to confuse the navigation systems of enemy aircraft.

The last day of broadcasting
This is the list of programmes broadcast on 1 September 1939. The final programme was followed by a tuning signal, then shutdown. PDF file.