Complex sentence: Back in London, he attempted to get his reports published in the Communist Party press to no avail and left the Party embittered with communism, writing about events in Hungary for "The Daily Telegraph", much to the chagrin of his former communist colleagues.
Split into simpler sentences: Back in London, he attempted to get his reports published in the Communist Party press, but to no avail and left the Party embittered with communism. Instead, he wrote about events in Hungary for "The Daily Telegraph", much to the chagrin of his former communist colleagues.