I wasn't aware of it until now, and I was surprised to find out that it took until 1991 for a Briton to fly to space - and with the Russians/Soviets no less, not with the Americans. But, if you look at https://en.wikipedia.org/wiki/Timeline_of_space_travel_by_na..., it looks like the Soviets recognized the propaganda value of giving a ride into space to citizens of "allied" nations (putting it in quotes because the Eastern European nations weren't really given the choice if they wanted to be USSR allies or not) much earlier than the Americans. When the US took West German Ulf Mehrbold into space with them in 1983, the Soviets had already done the same for ten (!) foreign nationals, including East German Sigmund Jähn in 1978 and Frenchman Jean-Loup Chrétien in 1982.

OK, to be fair, the US simply didn't have any crewed space launches between 1975 and 1981, that probably goes a long way to explaining this disparity. But still, once they started taking foreign citizens with them, I would have thought that Britain would be among the first on that list. Between 1984 and 1985 there were a Canadian, a Saudi, someone from the Netherlands and a Mexican, and then there was a long pause until 1992, presumably because of the Challenger disaster.