Tommy Flowers, the electrical engineer whose ground-breaking work in engineering culminated in the design and build of the world’s first ever large-scale programmable digital computer, has been commemorated with an English Heritage Blue Plaque at his former workplace, the charity announced today (6 September). The new plaque marks Chartwell Court, a monumental three-storey building in Dollis Hill. Now converted into flats, this is the former Post Office Research Station is where Flowers was given freedom to research and develop ideas, and where he designed, built and tested the computer – known as ‘Colossus’.

In 1941, he spent a brief time posted at Bletchley Park in order to assist the code-breaking teams there, including the mathematical genius Alan Turing. It was after this secondment that Flowers and his team set out to build an all-electronic machine. After just eleven months, and using mostly old telephone circuitry, ‘Colossus’ was successfully demonstrated at Dollis Hill in December 1943. The problem of thermionic valve failure caused by temperature fluctuation was avoided by the simple expedient of keeping the machine permanently switched on: this was Flowers’ ‘lightbulb moment’.

Kenneth Flowers, Tommy Flowers’ son, said: “My dad would be really pleased to have a blue plaque awarded to him, especially here, on the site where he and his team created Colossus and where he spent most of his working life.” 

Blue Plaques Panel Member, Dr Simon Chaplin, said: “Colossus undoubtedly had a huge impact on the outcome of the Second World War, saving countless lives. Beyond that, Flowers revolutionised the way we approach computing and his extraordinary achievements laid the foundation for modern-day computers and helped shape the digital landscape we know today.”

BBC Radio 4 Broadcaster, Paddy O’Connell, said: “My Mum worked for Tommy and she always wanted to tell the world about him. He was an unsung hero due to the secrecy that surrounded Bletchley Park but many features of the modern computer were present in his Colossus on which she worked eight-hour shifts.  I hope this plaque will make someone passing by check their smartphone and wonder how it all happened.”

Following its transfer to Bletchley Park by lorry – and despite it being, in Flowers’ words ‘a string and sealing wax affair’ – the first Colossus was deciphering the most sophisticated German codes within a fortnight. Flowers and his colleagues then quickly delivered Colossus Mark II, which was brought into operation five days before D-Day in June 1944. As the fastest code-breaking machine constructed during the Second World War, it has been convincingly argued that Colossus Mark II gave the Allies a crucial advantage over Germany: General Eisenhower believed that, collectively, the work at Bletchley Park shortened the war by two years.

The English Heritage London Blue Plaques Scheme is generously supported by members of the public.