Park made a strong speech at the Labour Party conference in 1958, which was highly critical of the leadership of Hugh Gaitskell.

Park's attendance at the Trade Union Congress and successive Labour Party conferences, coupled with his ability to impress with speeches, led to a degree of popularity.

Park was outspoken on several issues, including British diplomatic support for the Vietnam War and the incomes policy instituted by Wilson.

In 1969, he was one of the key figures who backed up those such as James Callaghan, who urged Wilson to drop the proposed Trade Union reforms of "In Place of Strife", a struggle which was successful.

Park decided to stand down at the 1970 general election, which other Labour MPs thought was because he knew defeat was inevitable; his seat indeed fell to the Conservatives.

He was not selected for Goole when a vacancy arose in 1971, nor for Batley and Morley after the retirement of the ailing Sir Alfred Broughton, nor for Penistone in 1978, all seats where he was thought to have a chance.