Plus of course even more than nowadays the primary user of computers was the government, particularly the military and intelligence services. So a computer user in the 1970s would likely have worked somewhere like GCHQ in Cheltenham (the equivalent of the NSA, who unbenkwonst to anyone except the high levels of the British government were continuing the work of Bletchley Park, and who invent RSA encryption long before RSA did), the army research HQ at Fort Halstead in Kent, and the nuclear weapons research institute at Aldermaston (and the associated nuclear power research institute in Harwell, south of Oxford). Both of these last ones are close to the Thames Valley and may have influenced the tech industry there? (I grew up right next to Harwell, and there is still a big private research park there, though the Harwell itself shut down in the 1990s)