Hi,

My wife and I will be traveling to London for 4 days in the middle of
this month, then back again for 2 days after a week in France. We will
be staying at the Docklands with a friend, and during the day going to
central London and moving around within the city - by bus and the tube.
We might make a day trip to Cambridge but it is not certain.

What is the cheapest way to use public transport for this short period
of time and from the Docklands as a base? Should we bring passport
pictures to get a travel card? Or is pay per ride going to be cheaper?

Thanks in advance.