While the chances that your ancestor had nothing to do with the British Cabinet, and you're British interests predate the 20th century, you may still find this presentation of interest.
Mark Dunton, The National Archives’ contemporary records specialist, explains how anyone with an interest in modern history can get the best out of the Cabinet Papers online resource. This provides access to historical records of the key episodes in 20th century British and international history. Mark also discusses the historical development of the Cabinet, how it works, and the main record series.
Don't be put off by the rather shaky and dull introduction; Dunton soon warms to his topic.