As Flowers remarked, at the outbreak of war “he was possibly the only person in Britain who realised that valves could be used reliably on a large scale for high-speed computing.

[3] The "Counter" project was abandoned but Turing was impressed with Flowers's work, and in February 1943 introduced him to Max Newman who was leading the effort to automate part of the cryptanalysis of the Lorenz cipher.

This was a high-level German code generated by a teletypewriter in-line cipher machine, the Lorenz SZ40/42, one of their Geheimschreiber (secret writer) systems, called "Tunny" (tuna fish) by the British.

Flowers and Frank Morrell (also at Dollis Hill) designed the Heath Robinson, in an attempt to automate the cryptanalysis of the Lorenz SZ-40/42 cipher machine.

[2] Flowers countered that the British telephone system used thousands of valves and was reliable because the electronics were operated in a stable environment with the circuitry on all the time.

Welchman preferred the views of Wynn-Williams and Keene of the British Tabulating Machine Company (BTM) who had designed and constructed the Bombe and wanted Radley and "Mr Flowers of Dollis Hill" removed from work on Colossus for "squandering good valves".

[11] Flowers gained full backing for his project from the director of the Post Office Research Station at Dollis Hill, W. G. Radley.

The Mark 1 Colossus operated five times faster and was more flexible than the previous system, named Heath Robinson, which used electro-mechanical switches.

The first Mark 1, with 1500 valves, ran at Dollis Hill in November 1943; it was delivered to Bletchley Park in January 1944 where it was assembled and began operation in early February.

[18] The government granted him £1,000 payment which did not cover Flowers' personal investment in the equipment; he shared much of the money amongst the staff who had helped him build and test Colossus.

[32] On 12 December 2013, 70 years after he created Colossus, his legacy was honoured with a memorial commissioned by British Telecom (BT), successor to Post Office Telephones.

The life-size bronze bust, designed by James Butler, was unveiled by Trevor Baylis at Adastral Park, BT's research and development centre in Martlesham Heath, near Ipswich, Suffolk.

[33] On 29 September 2016, BT opened the Tommy Flowers Institute[34] for ICT training at Adastral Park to support the development of postgraduates transferring into industry.

The institute focuses on bringing ICT-sector organisations together with academic researchers to solve some of the challenges facing UK businesses, exploring areas such as cybersecurity, big data, autonomics and converged networks.

The launch event was attended by professors from Cambridge, Oxford, East Anglia, Essex, Imperial, UCL, Southampton, Surrey, and Lancaster as well as representatives from the National Physical Laboratory, Huawei, Ericsson, CISCO, ARM and ADVA.