Can you suggest any useful resources for listening and/or reading practice?

Obviously past papers are key for practice at GCSE. Even old style practice papers are still useful. However it is not enough to just get answers wrong and move on. It is more useful to look up all the vocab you were struggling with and consolidate before trying the paper again. Beyond past papers, films are a great resource for listening. Either watch French films with subtitles (which will help your reading as well) or English films that you know really well (e.g. Harry Potter) and watch without subtitles. Also listening to the news is helpful (TF1 20H is a good website). There is even a news website which slows down the pace of the French so it is more accessible (wwww.newsinslowfrench.com). Also you could download a French news app (for example Le Figaro) because even if you don't read the whole article, the headlines will pop up on your screen every hour.