Running Routes: Suggested running routes in London

I'm going to be in London for 5 days next month and wondering if anyone could share thoughts/tips/suggestions for running routes...I'm staying in the Bloomsbury/Covent Garden area and looking for 4-6 mile runs on weekdays and maybe a 12 miler on Sunday. I am somewhat familiar with London but not intimately so... any tips appreciated. I'm an experienced "city street" runner in Manhattan but again, not terribly experienced with running on the "other side" of the road as I presume would be the custom.

If you are accustomed to looking to the left before you cross a street, you can be flattened by cars driving on the "other" side of the street.  However, the kindly souls who look out for the welfare of London residents and visitors paint the words "Look Left" or "Look Right" on the street surface, which is especially helpful for pedestrians crossing one-way streets.  Be aware of traffic, of course, but don't worry too much because of the helpful street markings.

 For you, the big decision is whether you want to ride a train or tube to your running destination, or start from your hotel.  If you start from your hotel, you should carry a map because the streets aren't exactly a grid.  However, you could run west on Oxford Street to the largest in-city park, Hyde Park, which is quite nice for runners, with good people watching, gardens, etc.

 If you are willing to take the tube out to the "suburbs," remember that some of the Thames still has ox-paths alongside the river, which could be a nice and scenic out-and-back or loop.  I can't recommend one in specific, and suggest you do more research, but I remember that there is an ox-path along Richmond-Upon-Thames, for example.

I should add that for the 3 parks it's 7 and a bit miles, but you only cross a couple of roads near Hyde Park corner and Buckingham Palace.