On one side, Flowers Close in Dollis Hill looks like a normal residential road, all brick houses and maisonettes. On the other side, you're faced with this:
Whether you consider the architecture to be a monstrosity or a delight, the building has a fascinating history, linked to the codebreakers at Bletchley Park. It's the former Post Office Research Station, where telecommunications research took place.
The Engineer has an account of what the building was like inside on its opening in 1933, full of 'specially-equipped laboratories' — like the Apple HQ of its time, we imagine.
The Colossus computer, the world's first programmable electronic computer, was created within these walls. Tommy Flowers, an engineer from Poplar, and his team, designed and built a cipher machine much more complicated than those used previously. Colossus was then used by the codebreakers at Bletchley Park to decode messages regarding German defence tactics, including messages sent between Hitler's office and army generals in battle, helping the Allied Forces to plan their D-Day approach and bring the war to an end. BT has more of the technical details of Colossus, if you fancy getting your head round them.
The machine weighed around a ton, so moving it to Bletchley Park wasn't a decision taken lightly (pun intended). At the end of the war, 11 machines were in use, and all but one were destroyed on Churchill's personal orders. The remaining one was taken to GCHQ in Cheltenham. A replica is on display in Bletchley Park.
The UK's speaking clock was also developed within this Dollis Hill building in the 1930s, and in the 1950s, ERNIE (Electronic Random Number Indicator Equipment — and apparently the inspiration for a Madness song) was created based on the Colossus research. ERNIE's job was simpler than Colossus's; randomly generating the numbers for the government's Premium Bonds scheme. The fourth incarnation of ERNIE is still used for this process today.
The building remained in use until 1967, when its operations were moved to Adastral Park in Suffolk. Today, it has been carved up into luxury apartments (you're looking at £425,000-£450,000 for a two bed flat), officially known as Chartwell Court. Flowers Close was built as an access road, named after Colossus engineer Tommy Flowers.
Hear computing pioneer Dame Stephanie 'Steve' Shirley talk to the British Library about the work she did at the Post Office Research Station, including her recollection of the words "Research is the door to tomorrow" over the entrance, and sexism in the work canteen.