Complex sentence: There is a ten years gap in the books on Widmerpool's sex life until, in the chapters describing the later stages of the Second World War, he is seen to admit to picking up "tarts" during the blackout.
Split into simpler sentences: There is a ten years gap in the timeline of books when Widmerpool's sex life is not mentioned. Then, in the chapters describing the later stages of the Second World War, he is seen admitting to picking up "tarts" during the blackout.