I'd just like to point out that there are a large number of US academics who come to the UK either regularly or occasionally to do research for their books and journal articles, and who probably enter as general visitors. I know several professors of English Literature who come to do research in the British Library or at the Bodleian, etc. They are not usually on sabbatical (as people on an academic visitor visa are), they just take a couple of weeks during the summer break to do the next bit of research. They would almost never make any money from publishing their research (indeed, sometimes academics have to pay a fee to a scholarly journal to cover costs), and they don't get any extra pay from their university employers.
How would these people be affected by this ruling? Anyone who is a professor of English Literature or British History, etc. could be affected ... surely the UKBA wouldn't want to shut down research on Shakespeare, Chaucer, Churchill, etc.?