https://nrich.maths.org/ - the NRICH Maths Site. Click on Stage 3 + 4 - new problems each month - Cambridge University,
England, UK - resource notified by Mrs. Jennifer Piggott, University of Cambridge Faculty of Education (Cambridge, UK).
9th May 2005: Our thanks to Kaiya Williams who has sent in details of this amazing resource ..... GCSE: Years 10 and 11 ..... See the "Pupil Text Books" and "Practice Books" for the basic material. Note their disclaimer: "The material is made available through the CIMT for downloading and dissemination for NON-PROFIT MAKING PURPOSES ONLY."
Also includes teacher support resources but certain aspects of these (like revision tests) require "passwords" [their site says "passwords are not normally available to individuals who are not part of an educational institution"].
Homeschooling parents should be able to make use of a *huge* percentage of this resource however - together with their Year 1 to 6 resources (see Maths Key Stage 1 for this and other free Maths resources available) and Key Stage 3 resources (see Maths Key Stage 3) it includes virtually everything most parents will need. This free resource has been created through a collaboration between the Peto Institute in Budapest, Hungary, and the Centre for Innovation in Mathematics Teaching at Exeter University, England.