L.R.
Yep, let the baby sleep whenever, wherever. Going back to a hotel room for designated nap times would indeed crush the adults' day out and would be useless too -- going back may well wake her up too much and when you arrive at the hotel she may not be willing to go down! You might need to pull the stroller over to a quiet area when she seems to be getting sleepy, to help her fall asleep, but you still will be seeing the sights or eating your croissant so you're still enjoying the trip!
Sleep while in motion isn't as beneficial as in a crib? I never heard that (and my daughter had plenty of "car naps"), but as you say, it's just for two weeks. The benefit of traveling with very young infants is that they are not mobile and can't run around -- and she's so young she's mostly about eating, sleeping and soaking up things around her. Her schedule will be off so let her sleep when needed and be prepared for some early mornings for you. Have fun. We've traveled overseas with our daughter every year since she was born and it does get easier and easier. Infancy and from about 4 onward are better than toddlerhood where they need naps but resist (and don't just fall asleep like babies will)!
By the way-- Enjoy England. We go annually to see the relatives. Britain has far more "family restrooms" and nursing rooms in places like highway rest stops, department stores, etc., than we do here, and remember that almost every department store and every tourist site (castle, palace, historic site) has a cafe so you always have a place to chill for a while if she's sleeping or you need a bite. Also, if you need a doctor, they are free and so are prescriptions! The down side on England with a stroller -- everything is in buildings that were built long before anything like "accessibility" so you will be bumping the stroller up and down strange steps indoors at times. But you'll have fun!
