Janisi,

Sorry about that. I hadn't read the rules properly and already had apologised on the other topic and do so again on this one. Won't happen again.

I agree about not trying to cover too much in one trip. For London, I suggest Citadine's Holborn. It's in a central location, near the Tube, and you get a kitchenette so you can make your own breakfast or simple dinner, using the nearby Sainsbury's, which has lots of choices for heat and eat.
I visited England with an English friend for three weeks, in November 2001, of all times. Other than London, where we stayed at the Citadine's, we picked up a car at Heathrow and took off to visit her relatives who lived in great places: Salisbury, Beeminster Dorset, Mevagissey Cornwall, Portsmouth area and the channel island Guernsey.
While en route, we stopped at Lyme Regis. The highlights were Salisbury, for the amazing cathedral with the tallest spire (1566 I think) in Britain, and the beauty of the old town on the river; the Eden Project and Lost Gardens of Heligan in Megavissey; the charming twisty streets overlooking the Cob in Lyme Regis; visiting a village church near Beeminster with grazing sheep sand inside a tattered flag from World War 1; hearing cannons on Remembrance Day in Guernsey.
In London, we saw nine plays; went to the Tate Modern three times (wonderful cafe with views of St. Paul's); walked to the Sir John Soane museum nearby and stayed most of the day: did the Hop on Hop off two day bus for an overview of the city; did the train in Canary Wharf; St. Paul's was inspiring, especially the photo display showing the bucket brigades putting our fires there during the Blitz; walked around a lot, went to the bookstores by Charing Cross; rode on the London Eye; took a Thames river cruise...
And more that escapes me right now.
You have a wonderful adventure awaiting you. And I was pleased that with a few exceptions, the food was very good, although pricey. Many pizzerias in London...

An option that worked well for me was flying into Edinburgh and staying there for a few days, taking the train to York (another couple of days), and then to London for the remainder. Many places are easy day trips by train from London (Bath, Stonehenge, Oxford, Cambridge, Canterbury, Windsor to name a few).