Stick with it until about 2:35, anyway. It suddenly goes all 16th C (see below).
Richard Thompson was a founder of Fairport Convention, the other English electric folk band of the early 70's, and much better known in America than Steeleye Span at the time. I never liked them much, as Sandy Denny's voice was just a little too...something for my taste. The difference has got to be subtle, because it is much like Maddy Prior's.
I never quite forgave Thompson for playing the Joni Mitchell tribute concert, thinking "you need to get out of this." But ethereal voice, unusual tunings, I suppose I can see how you'd have to be on board with Joni if you're Richard. Some magazine - it may have been Playboy - asked popular musicians in the early 2000's what the "top popular songs of the millennium" had been. Everyone else stretched their musical knowledge back a few decades, or maybe a century. They may not have known what a millennium was, or had little idea of history. When I sang old folk songs years ago, many people, even ones you would think quite savvy, had a category "old music" in their brains that covered everything from Depression-era bluegrass backward. They might have the additional bit of knowledge that "Greensleeves" was really old.
Thompson took it seriously and did an entire album on it, starting with Sumer is icumen in.
(A song which gave rise to my best literary off-the-cuff joke ever - incredibly brilliant - but gets completely ruined by having to explain it. The punch line is "Loude sing Marcoux." See, that doesn't help you any, does it?)
Here's a Fairport Convention tune from the last album he did with them, and the only one I was familiar with until years later.