The Changing of the Guard may not take place under adverse weather conditions. In such cases, the tour will visit the Horse Guards for a photo stop instead.
If you selected the tour with the Thames boat ride, you will be given a voucher that you must redeem at any ticket office. The one-way ticket is valid until the last boat from Westminster, Embankment, or Waterloo to Greenwich or vice versa.
Check the official website for the daily opening hours and gallery closure dates prior to your visit.
Check https://bit.ly/42KNtUE for the boat route and timetable.