Conversation so far:
What is peerage?
Labour peers to aid political work in the House of Lords.
How was it reformed?
The Peerage Act 1963, allowing lifetime disclaimer of peerages.
What was disclaimer of peerages?
Benn was the first peer to renounce his title.
Why did he renounce his title?
Benn automatically became a peer, preventing him from sitting in the House of Commons.

Question: Why did he automatically become peer?
Self-contained rewrite: Why did Tony Benn automatically become peer?