The Knowsley North by-election, 1986 was a parliamentary by-election held on 13 November 1986 for the British House of Commons constituency of Knowsley North.
Labour retained the seat with well over half of the votes, while the SDP-Liberal Alliance finished runner-up by attracting more than a third of the votes. Although the Conservative government at the time was just months away from a third successive general election win, the Conservative candidate in this by-election attracted just over 6% of all votes - reflecting the Conservative Party's low popularity on Merseyside, which had some of the highest levels of unemployment in the United Kingdom largely due to the monetarist policies to tackle inflation.
The seat had become vacant on 1 October 1986. The constituency's Labour Member of Parliament (MP), Robert Kilroy-Silk (born 19 May 1942) resigned his seat to pursue a media career. He did this by being appointed Steward of the Manor of Northstead, a notional offices of profit under the Crown, which is used to permit MPs to vacate their seats.
Kilroy-Silk had been an MP since the February 1974 general election. The constituency he originally represented was Ormskirk. That seat disappeared in a redistribution and Kilroy-Silk moved to the new constituency of Knowsley North in 1983.
He returned to politics in 2004, becoming a Member of the European Parliament (MEP) for the East Midlands, initially with the United Kingdom Independence Party.