Meanwhile, German health authorities scrapped their own version of a similar app in favour of the Apple and Google version after running into similar iPhone issues in April and have since released their contact tracing app.
The NHS is still working on its second version of the app, which may not be ready until winter, according to health ministers.
Giving a talk at London Tech Week on Tuesday, Mr Gould said his team started on its version of the app early in the coronavirus pandemic and then spun off a second team to work on the Apple and Google version as a back-up.
He said: “The combination of being willing to set up a team swiftly to try out a new technology, to run parallel tracks so we could see both [apps] in action and then to test substantially I think were the right things to do.
“But the last lesson on this is that tech is difficult and unpredictable. It would have been very simple to have not done it or not done substantial testing and just produced [an app] and put it out there.”
Mr Gould, who is still advising on the development of the Apple and Google version of the app, said it was right that it be taken over by the NHS team developing the overall test and trace system, describing them as “brilliant”.
He added: “It is always a wrench when you have been working on a project and you have to hand it over.”