While wearing a kippah when in the Queen's presence is done by Jewish men
who visit her, wearing a hat is not. No matter what your citizenship,
wearing a hat in Her Majesty's presence would be a slap in the face, and I
do not believe it is defensible to say that Jews should do so. As long as a
man does have a kippah on, wearing a hat is not necessary, and it would be
disruptive, at best, to act with such a lack of Derech Eretz (respect) for
the Queen, and it would be harmful to the Jews in England. As such I can
not imagine someone actually arguing that as an American or Israeli Jew,
they would not take off their hat. (Of course this is not to say that they
should be actually "bare headed")
Nechama Cox
London, England
nechama@borealis.com