Well, GCSE is actually junior high school age (14-16), rather than American high school age which is more or less covered by A-levels.
If I recall correctly, when doing GCSEs, we studied some Shakespeare (MacBeth, although it had a parallel text in contemporary English), metaphysical poetry (John Donne, Andrew Marvel), Shaw's Pygmalion, and Thomas Hardy's The Mayor of Casterbridge. I expect I must have also read some kind of contemporary literature as well, but I don't remember.
For A-level I remember that we did more Shakespeare, Hamlet and Richard II, but not with the parallel text, Dickens's Great Expectations, the Romantic poets (Samuel Taylor Colerdidge, in particular), some contemporary novels (Atwood's Surfacing and Ackroyd's Hawksmoor), as well as Ibsen's Doll's House (I think the only thing that had been translated) and a collection of African poetry.