In 1974, at the funeral of his cousin Dominic Elwes who had committed suicide, after a sententious speech by John Aspinall, Rennell infamously "went up and gave  Aspinall the most useful punch in the face you have ever seen." He succeeded his uncle as 3rd Baron Rennell in 1978, and took the Conservative whip in the House of Lords.
At Dominic Elwes' funeral in 1974, after John Aspinall gave a lengthy speech, Rennell delivered a notable punch to Aspinall's face. He then succeeded his uncle as 3rd Baron Rennell and became Conservative whip in the House of Lords in 1978.