Mary Anne, thanks - I get it now. And shame on me for not spotting the location originally! I just figured leicester square because you get a lot of preachers there. Good luck with the entry.
It's the big sign behind him that says "15th Century." I was struck by the juxtaposition of the long-ago date and the modern-day preacher. And barely visible along the right margin, you can see the name of the location: Tower of London.