7.5 days for Lake District and London - appropriate breakup??

It depends what's on your list of "must-see" attractions in London, and how thoroughly you want to see them. Someplace like the British Museum or the Tower of London could easily take a half day or even a full day - or you could be in and out much quicker than that, if you're organized and have an idea going in about what exhibits you're most interested in seeing.

Keep in mind, though, that London is very large and spread out, so even if you're budgeting only a short amount of time per attraction, it could be difficult to see more than three places per day, once you account for the travel time between them.

Thanks khbuzzard

We have decided to move one extra day to London and move from Lake District to London on 20th June itself (instead of 21st June). Though now I am a bit worried if 2 days will be enough for LD, especially of the weather turns bad.

We would have our base in Coniston and would have a car, could you guys suggest an ideal itinerary for two days? We are not into serious hiking, the idea is to drive and stroll through the area, walk a bit, sit back, relax and enjoy the sights and the local culture.

It's unlikely (though not impossible) that you'll have bad weather for two days straight. That doesn't happen very often in that part of the world at that time of year.

Since you're looking for relaxation, I'd say that unless there's something you've really got your heart set on in one of the other Lake District towns (e.g., if you're interested in the various Beatrix Potter attractions), you're probably best off sticking to Coniston and the areas close by, rather than trying to devise an itinerary that covers the whole of the Lake District. You can do a Google search for "Coniston walks" and find pages like this one with ideas of easy strolls to take. Or stop by the Coniston Tourist Information Center and they should be able to help you as well.

If you find you want a larger town to explore, you could head over to Windermere, around a 30-minute drive away.

The kielder lectures are great we went last Oct.
For a quirky place to stay Wildnorthumbrian is about a 20min drive .

Coniston is a lovely place and there is lots to do right around that area. The author, John Ruskin, lived in Brantwood House just on the other side of the lake from the town and it's a beautiful, typical Lake District style home in a lovely setting. Sawrey, where Beatrix Potter's first farm is located, is just over the hill on the far side of the lake as well. Right next door is the Tower Banks Arms pub that she drew and included in several of her famous picture books - it's a quintessential pub and very typical of the area. Excellent food!
Wray Castle is another lovely country home in the area that is worth visiting. Just north of there is Grasmere - cute but ubertouristy. The walk from Rydal Water to Grasmere is one of the nicest walks in the Lake District. Wordsworth lived right there and you can visit both Dove Cottage and Rydal Mount, two of his homes. There is a small museum about him that is of interest as well.
If you have more time other parts of the Lake District are spectacular as well - Buttermere is my favorite lake to walk around and the tiny town of Buttermere is well worth a visit - a great place to eat is the Fish Inn. Keswick is a nice town to explore and you can ride out onto Derwentwater on old wooden launches that stop at several places around the lake where you can get off and walk. Castlerigg Stone Circle is well worth your time...it's a lovely ancient site with amazing views. Sunrise and sunset there is worth waiting for.
I recommend the movie "Miss Potter" about the life of Beatrix Potter...it's dramatized (Renee Zellweger and Ewan McGregor) but very good! It covers the part of her life from when she first published Peter Rabbit until she settled in the Lakes and bought up many farms there in order to preserve them. There is a really good British mini-series filmed almost entirely in Coniston called "The A Word" about a family who discovers their son is autistic. It will give you a really good feel for the town and area.
There is so much to see and do in the area! If you can keep your 3 day plan I think you'll be happy that you did!

Thanks a lot Anita for all the wonderful suggestions. This really helps us planning our time judiciously in the Lakes.

Regarding adding a day to London, if we go by our original plan, it will actually be only 2.5 days in London excluding Harry Potter and Windsor Castle day trips. Within this also, on the last day we have a 9:30 PM flight from Heathrow, so will have to leave for the airport by evening itself, so maybe I should count 2 days only for the city attractions, which may or may not be enough for covering all the places we want to cover there.

I feel it prudent to err on the side of caution for London by making it 3 days and 2 days would possibly be just about OK for LD considering we are not too keen on visiting all the Beatrix Potter and Ruskin attractions over there.