The proper adjective from of the United Kingdom therefore is either "U.K." or "British", not "English." Take a look at the following examples:
- the British government/the U.K. government (o)
- British English (o)
- the British Parliament/the U.K. Parliament (o)
- a British scientist (o)
- an English scientist (x, unless you are emphasizing the fact that this person is from England)
- the English government (x)
- the English Parliament (x)