Britannia was built at Crewe, completed on 2 January 1951. She was the first British Railways standard locomotive to be built and the first of 55 locomotives of the Britannia class. The locomotive was named at a ceremony at Marylebone Station by the then Minister for Transport Alfred Barnes on 30 January 1951.
The BR Locomotive Naming Committee were determined not to use names already in use on other locomotives. They tried to observe this by not selecting the name Britannia for use on 70000 because it was already in use on one of the ex-LMS Jubilee Class locomotives, but Robert Riddles overruled them and the Jubilee had to be renamed.