It rather depends what you are interested in.
Scenery the south downs, the Peak district, the lake district, highlands of Scotland and Wales are all spectacular.
history start with Stonehenge and Avebury. Salisbury Cathedral inside is amaxing. York is a city well worth a visit. Midlands is great and Trentham village near Stoke on Trent is fun to walk round and there is a fab pie shop . Monkey World in Dorset is doing marvelous work for wildlife and is close to some amazing scenery Durdle door, Lulworth cove, chessil beach among other things.
Petworth house and Arundel castle are beautiful and have the benefit of towns that are full of character.
any of the wetland wildlife trust settings are fantastic for bird watching.
Burley in the new forest has lots of unusual shops with a witchy theme.
London museums and galleries are just awesome you will never be able to see them all in the time given. Tate modern and Tate with the clore (not sure of spelling) gallery with the massive Turner collection is unmissable.
If you are interested in literature then the old curiosity shop can be found at the bottom of portugal street in London and there is a quirky museum close to that called the soames museum.
There is so much to discover in the UK and to do it all in 2 weeks impossible. I would plan more than one visit and explore each one.