Questions re: academic research

I hope you can help me figure out exactly what I need to do, as I'm really confused and seem to be getting conflicting information.

I'm an American, currently enrolled in a Ph.D program at an American university. I am writing my dissertation on a building in England, and came over to England in February to live in Yorkshire and do research for four months. I was planning on returning to the States in early June, but I have since received several fellowships and grants that I applied for last fall, which means that I now have enough money to continue my research in England for another 16 months, which is exactly what I want to do.

Obviously, this is going to extend my stay over the six-month period that I was admitted for. What kind of visa do I need to get for this kind of stay? The info on the British consulate website seems to indicate that "academic research" visas are for people who actually lecture/teach (I'm just a graduate student). It also said the scheme for short-term research was discontinued and that I should enter under the work permit scheme. This makes no sense, since I won't have an employer in the UK. I am getting money from American grants agencies.

My questions, then, are
1) What kind of visa do I need to get?
and
2) Can I do this from England, now that I'm here? Do I really have to fly all the way back to the States and go to the British consulate in NYC (home is in Baltimore)?

Many thanks for your help!