Where to enter the city of London.

[halflive]

Hello,
We are planning a summer holiday in England. After a leap of 20 years this will not be our first visit. But it will certanly be our first visit with a sidecar, a right hand sidecar.
Driving on the left hand side won't be the major issue, The country lanes and towns are crammed with roundabouts. The only issue i ever had was taking a right hand turn on a T junction. Being acquainted to taking the short turn i ended up standing nose to nose to a car.

Now my issue:
For my daughter it will be her first visit to England. And off course, we have to visit the inner city. But i like to avoid inner city's. Especially when the traffic is coming from the side i don 't expect it to.
When we fly to Londen, we always take the tube. Great, fast, cheap, no parking. This is the way i like to visit the City.
Is there a tube station, preferably not to far inside of the M25 where i can leave my sidecar for a day. It doesn't have to be your backyard, but i don't like to find the bike without wheels.
Preferably around the south side of London. We are coming from Dover and heading west, possibly in the direction of Oxford. I have been looking at Greenwich. It is a must seen, and not to far from the city by tube.

Thanks in advance.