"According to a document published by the UK government about Schedule 7 of the Terrorism Act, "fewer than 3 people in every 10,000 are examined as they pass through UK borders" (David was not entering the UK but only transiting through to Rio). Moreover, "most examinations, over 97%, last under an hour." An appendix to that document states that only .06% of all people detained are kept for more than 6 hours."
So yes, it does seem to be a bit of over the top heavy handed intimidation.