Sorry: I've been off-line.
My impression of the Telegraph BIG books is that the individual puzzles are not grouped or ranked but merely chronological. They do give the solutions. OK, they do not actually explain how the solutions fit the clues, but I am sure that if you persevere you will begin to recognise the constructs. Remember, the whole point is that they are meant to be a challenge! Plenty of people need help with solving crosswords which is why this forum exists, and many responses hint at or explain how the clues are decoded. Happy Puzzling!