Googlevideo has it online:
1000 Misspent Hours praises it and sums up by saying, "In short, this is an immensely satisfying film." Moria also likes it, saying, "This is regarded as one of the genuine classics of the genre. And it’s not hard to see why". DVD Journal calls it "a modest but effective gothy thriller of necromancy and deviltry that's a high point in British cinema".
There's a quote from Coleridge's The Rime of the Ancient Mariner in the film:
Like one who, on a lonely road,
Doth walk in fear and dread,
And, having once turned round, walks on,
And turns no more his head;
Because he knows a frightful fiend
Doth close behind him tread.
I'm surprised this one isn't better known.
10/3/2009:House of Mirth and Movies has a post.