Why couch your question in terms of "ashamed of" and "pusillanimous attitude"? I do not believe it is right to cast aspersions on the characters of people of whom you know nothing. For myself, although I do not seek being photographed, if I am in a public place then snap away - not being the most photogenic of subjects, they will end up unprinted!
Also, I have never been stopped by the police from taking photographs in London (they have no general power to do so) nor have I ever seen anyone so treated. The police may take an interest if you are near a government building (which in central London means just about anywhere), police officers being by nature or training drawn to unusual occurances, but once satisfied of what you are doing will leave you in peace.