Complex sentence: This included buying a new house and car and buying large rounds at the pub. This brought suspicion upon him and MI5 put him under surveillance, which led to other members of what was to be known as the Portland Spy Ring.
Split into simpler sentences: This included buying a new house and car and buying large rounds at the pub. This did bring suspicion and MI5 put him under surveillance. This led to other members of what was to be known as the Portland Spy Ring.