I enjoy riding in my Denmark jersey. People always look at me just a little longer than usual before realizing that I'm not fast enough to be a pro. Did fool one driver once, who asked me at a red light which race I was training for
I used to row for Royal West in Greenock, and their colours were/are the same as the Danish Flag. We never had any issues with it (except for people possibly thinking we were Danish during the Tall Ships Race) although that said, the Glasgow Rowing Club's colours are black red and yellow, and for a long time had what could have been mistaken for German flags on their blades (oars) (The colours came about as a result of a merger between the existing Glasgow Rowing Club and Glasgow Argonauts in 1983). They have changed it to a much snazzier design (with the same colours, obviously) now, but other than the odd comment, I don't think I ever heard of any problems with their 'German/Belgian' oars.
That said, it was Glasgow, not London,
There are 3 clubs that row on the Clyde in Glasgow, 'Glasgow' (the 'German' ones) who are in the Gorbals, but of the two that are based on Glasgow Green, Clyde and Clydesdale, I think it is Clydesdale that has their colours like a Scottish or Shetlandic (I can't quite remember) flag.