The site linked by Malcolm Douglas has a box with "Buy this book from..."
Abebooks, Alibris, Barnes and Noble, Amazon.
I went to Abebooks, and found the Halliwell book at Quartermelon, Stratford Books, etc., in the UK. Prices vary widely! One says Kessinger prints on demand.

At random from the Kessinger catalog I picked Shelley, "In defence of poetry..." In Abebooks, The Kessinger reprint showed up at several English booksellers, inc. Books2Anywhere.com, Quartermelon and TheBookCom.
I would go to Abebooks or Alibris, and find a seller in the UK and look for the lowest price. For some titles, prices were lower for some editions other than Kessinger reprints.