Complex sentence: Chatwin had hoped to read Classics at Merton College, Oxford, but the end of National Service in the United Kingdom meant there was more competition for university places, and Chatwin was forced to consider other options.
Split into simpler sentences: Chatwin had hoped to read Classics at Merton College, Oxford, but his plans were thwarted by the end of National Service in the United Kingdom. As a result, there was more competition for university seats, and Chatwin was forced to consider other options.