I was thinking of suggestions more outside of England.
That said, have you considered backpacking across the UK?
It's much safer than Europe, and is a good place to start if you've never gone backpacking before.
You don't have to worry about foreign languages, foreigners themselves (not being xenophobic, but foreigners, particularly Europeans, do weird things that can be quite distressing to the English. Particularly things like touching the hair of strangers and such), you know the Emergency Services, if you get injured then you have the NHS and don't have to worry about having an EHIC (You better damn well have one of these if you do go to Europe) or hospitals asking for upfront fees, you know the food (not likely to get the stuffs), you can continue to use your regular phone network, plus you are safer with money since you can use banks and cashpoints across the country for no additional fees, and you don't have to worry about exchange rates.
And should anything really go wrong, you can be damn certain you can get a bus/coach back to London and be home within a day.
And there's an unbelievable amount of things to see wherever you go, whether it's in the South, the North, Wales, Scotland or even Ireland.
And what would be really great for you is that you can purchase a
National Trust membership and that gets you into lots of places for free, whether they're castles, ruins, historic houses or more.
Given the amount to see and do in the UK, most people living here truly miss out on a lot.
I personally plan to do a camping/hiking holiday along the length of Hadrians Wall.
