What to see in London? Were do you start? Been there twice recently. First time did mostly outdoor stuff - Changing the Guard at Buckingham Palace, St. James's Park, Tower of London (via a boat trip), Big Red Bus tour, Harrods, etc. Second time, used tube and went to British Museum, Westminster Abbey, St. Paul's Cathedral, London Eye. Still to see Madame Tousseaud's, Globe theatre, Tate Modern, Albert Museum.... You get the picture?!!
English in Paris - Did not find it a problem and, after hearing the horror stories of rude Parisians, we did not find any. People were polite and helpful. An introductory "Bonjour" elicited English resposes - my accent is as atrocious as advertised! While English signs are not plentiful, we found them when necessary and French signs are not indecipherable. We went (one way) Eurostar from London and it is a fast city centre to city centre connection, but really quite a boring ride. The part of France you cover is ubelievably flat. Ever been to Saskatchewan, Canada?
A day trip to Paris is, however, a waste, in my opinion. Paris deserves much longer. If you see the Eifel Tower and the Arc de Triomphe that will be about it, and that is not all there is to Paris.