Harris became a political adviser when Labour came into government following the 1964 general election, firstly to Foreign Secretary Patrick Gordon Walker, and then to Roy Jenkins at the Ministry of Aviation, the Home Office, and then the Treasury until the 1970 general election when Labour lost power [REF].
Harris was a leading member of the "Yes" campaign for the 1975 referendum on whether Britain should remain a member of the European Economic Community, and was joint chairman of the publicity committee [REF].