Cross-linking to the YA thread, since Gwyneth Jones (
ISFDB,
Wikipedia) is a pretty prominent multiple award-nominated British sf/fantasy author, and I read her YA pseudonym fantasy titles (not these particular ones) from the school library bookshelf growing up:
Free from the author via KDP Select @ Amazon:
2 backlist YA modern urban sf/fantasy + horror hybrid adventure thriller novels written as "Ann Halam", originally out from Penguin's Puffin imprint and Orion Books