Are there any anthologies of pieces at about grade 8 level?
At up to grade 7 (which I'm working on now) the ABRSM publishes quite a number of different collections. But, apart from the exam books, there doesn't seem to be anything at grade 8.

Thanks.

If you don't already have them, David Willison's World Renowned Piano Pieces (Books I & II, published by Alfred Lengnick) are an indispensable starting point. Excellent variety of music, ranging from grade 5 to beyond grade 8: plenty to work on, and an awful lot to enjoy. Otherwise, it might be an idea to buy some old ABRSM selections from past Grade 8 exams - sounds uninspiring, but they have interesting repertoire (especially in the C section), and might be available at a knock-down price at a music shop.

Try having a look on musicroom.com. I typed in grade 8 piano and apart from the usual exam stuff a couple of books came up with repertoire in.