When you arrive in London from any destination or from Paris or Bruxelles by The Eurostar or train you will meet your guide and then get a day pass at St. Pancras, and catch the Picadilly Line to the station next to Harrods for a shopping time after lunch in that neighborhood, you will start a Walking Tour at the Wellington Arch.
Your Guide will walk you from Hyde Park, to Buckingham Palace, St. James Palace, Trafalger Square, Horse Guards training area, Downy Street, Westminster Abbey and Parliament and Big Ben. It will take about 3 hours.
Then you will jump on the yellow circle line to get a quick look at St. Pauls, and then you will cross the river to the Globe Theatre, back across the river to the tube, Circle Line again, down to the Tower of London and Tower Bridge. Back on the Yellow/Circle line to St. Pancras and you will stop by a local pub nearby around 6:00 Pm for dinner or a beer prior to Eurostar departing around 8:15 Pm back to Paris.
This tour is the best option for visitors who want to see the best of London in one day trip.