Complex sentence: One of the first to be arrested, in the early morning of 23 May, was Sir Oswald Mosley, whilst others arrested later included Admiral Sir Barry Domvile and Sir Reginald Goodall.
Split into simpler sentences: One of the first to be arrested, in the early morning of 23 May, was Sir Oswald Mosley. Others arrested later included Admiral Sir Barry Domvile and Sir Reginald Goodall.