Fawley Power Station, a partially operational power station and former executive office campus was used as the "Home Base" . Commissioned in 1971 and built on the western side of Southampton Water it had been used previously for films such as "Rollerball" and "Mission Impossible - Rogue Nation", as well as episodes of "Green Wing" and "Red Dwarf".
42 cameras of all different types were used just in the filming of the "Home Base" segments within the power station.
Several hundred people showed up to take the initial written test that the former spies had created to mimic the official IONEC exam given to prospective UK intelligence officers. They then identified their top 14 candidates using a selection system even the show's producers were not privy to.
The candidates were whittled down over the course of filming and the ex-spies revealed and relied upon many of the techniques that the official UK Intelligence Officer New Entry Course (IONEC) uses to train secret agents.