Complex sentence: Burgess was delighted, as were his Soviet controllers at the prospect of the information that would be available to him--the private secretaries saw all the overseas cables, Foreign Office reports and cabinet papers that passed through the office on their way to the minister.
Split into simpler sentences: Burgess was delighted, as were his Soviet controllers at the prospect of the information that would be available to him. The private secretaries saw all the overseas cables, Foreign Office reports and cabinet papers that passed through the office on their way to the minister.