There are three distinct reasons why this description of the group of competitors who are members of the British team is incorrect.
1) Competitors from Northern Ireland are included within the said group. However, Northern Ireland is not in Britain. It is in the United Kingdom (of Great Britain and Northern Ireland) normally abbreviated to UK.
2) The word "team" should not precede the abbreviation. "Team" should come after. "Team UK" (or "team GB") sounds like the utterance of a five-year-old who hasn't learnt to speak properly yet.
3) In what way are canoeists, cyclists, boxers, javelin throwers, etc. in the same team? Clearly, not at all. It is silly to suggest that they are in the same team.