Given that the Olympics will be on, probably best to forget about London this trip (Some would say better to forget about it altogether) and spend more time in Scotland. You could easily spend 3 months photographing in Scotland and still only have covered 10% of the most dramatic and scenic locations.
Some good advice in the contributions farther up the thread. Just one point in relation to Chairman Bill's first observation - about the weather. Don't be put off by the promise of mist, rain and low cloud on Mull, Skye or, indeed, anywhere in the north-west. That is, by far, the weather that produces the best photographs. The last thing you want on the Western Isles is sunshine. It is pretty much the opposite on the Northern Isles and down the east coast - where blue skies and sunshine can be usefully incorporated into your photography.
The midgies? Yes - worst on the west. But the preferred repellent by the Royal Marines is, believe it or not, a woman's skin preparation called Avon Skin-so-soft. Beats Jungle Formula and suchlike out of the park.
Enjoy your trip.