At the end of the episode, Steed attempts to repair Mrs. Peel's toaster, but on testing it, the toaster flies through the ceiling (somehow leaving the toast behind) and Steed remarks; "That's the first thing Britain's ever put into orbit".
The episode was first shown on 30 September 1967.
The UK's first satellite - Ariel 1 - had been launched on 26 April 1962. It was the first satellite from a nation other than the Soviet Union or the United states. It was followed by Ariel 2 on 27 March 1964, and Ariel 3 on 5 May 1967.
Ariel 1 and 2 were assembled in the USA, whilst Ariel 3 was the first satellite designed and built in the UK. However all three were launched by the USA, as was Arial 4, on 11 December 1971, and two others.
The UK became the sixth nation to launch its own satellite when it put "Prospero" into orbit, but that wasn't until 28 October 1971, so at time of Steed's statement he was quite correct.