Thanks for all the suggestions. We did the trip last weekend.

In the end we did The Cutty Sark and Royal Observatory using the River
Boat (that I never knew existed so extra thanks for that) from HMS
Belfast to get there.

But next time I must check the calender before we go. It was Chinese New
Year so Sunday was a free display about 2 minutes walk from the hotel.

Now I am really annoyed:-) The hotel room had more USB charging points
in it than I have in my house.

--
Adam