I will be in London during mid-week in February. There are several things that I want to do/see that I can purchase tickets for beforehand on-line. For instance, I definitely want to "fly" the London Eye and see a popular play (maybe Producers or Mary Poppins). Should I purchase tickets now or when I arrive in London? Not sure what the lines will be like that time of year. I'd like to wait until I'm in London, if possible. I'm really not an itinerary type of person. Thanks for your input!