Certainly is. I remember seeing the job ad and wishing I had at least one of the necessary skills!
Good material in here for a pub quiz question: Tim Peake was the
(a) 1st
(b) 2nd
(c) 4th
(c) 7th
British astronaut.
Answer: https://en.wikipedia.org/wiki/British_space_programme#British_astronauts
The interesting thing about those who became US citizens, it was because you could not be an astronaut with NASA unless you were.