I see London...

Exactly six weeks from today, we'll be wheels-down in London, starting our 16-day tour of the British Isles including this fab 12-day cruise on the Oceania's Marina (same ship as last year).  As previously reported, the day we land (at 8:45 a.m.), is the day of the Queen's 60th Jubilee flotilla on the Thames. On such a momentous - and crowded - occasion, we'll be doing well to find our way to the hotel, check our bags, gobble some fish & chips and head to the River for a glimpse of the Royals. On Monday, the real sight-seeing begins with a double-decker bus tour of London. But, which one? There must be a dozen different lines. Any suggestions?