Changing of the Guard was an embarrassment when I last saw it in 2012; probably hasn't improved since then. London Eye; not worth the time IMHO. If you want a view climb to the top of St. Paul's Cathedral and kill several birds as it were; the 17-19th C graffiti on the inside of the dome is interesting. Westminster Abby is worth some hours for those interested in history. Houses of Parliament: debatable. Only an early Victorian construction after all.
BritishMuseum is sensory overload, but the same is true of the others such as V&A, National Portrait Gallery, Tate etc. The Science Museum might be more enjoyable for most of us.
I suggest you plan out your steps as completely as you can: for example even where you will eat and when. Trip Advisor for recent feedback and info. There are many good places, but so many mediocre (as is true everywhere) that it's worth doing the research rather than missing out and time is clearly of the essence when overseas. Even if you don't care so much about what you eat, what kind of place you eat it in, how long it takes to get there and to get served and what it costs, can be very different indeed.
Even more true for transport and accommodations.