Beaumont - who later in life was a circuit judge in the UK - is most scathing about how partition affected the Punjab, which was split between India and Pakistan.
"The Punjab partition was a disaster," he writes.
"Geography, canals, railways and roads all argued against dismemberment.
"The trouble was that Muslims, Hindus and Sikhs were an integrated population so that it was impossible to make a frontier without widespread dislocation.
"Thousands of people died or were uprooted from their homes in what was in effect a civil war.
"By the end of 1947 there were virtually no Hindus or Sikhs living in west Punjab - now part of Pakistan - and no Muslims in the Indian east.
"The British government and Mountbatten must bear a large part of the blame for this tragedy."