Raymond Gower Conservative John Smith Labour A by-election was held for the British House of Commons constituency of Vale of Glamorgan on 4 May 1989 following the death of Conservative MP Sir Raymond Gower.

The result was a Labour gain, the party's first by-election gain of this parliamentary term, which came at a time when it was starting to match and even overtake the Conservative government in the opinion polls, just after the controversial poll tax was announced.

The swing of 12.35 was significant as if repeated at the next general election would have resulted in Labour winning power.

[1] The result was reported by The Glasgow Herald as being a "humiliation" for both the Social and Liberal Democrats and SDP, the two centre parties which had emerged from the former SDP–Liberal Alliance.

In the wake of the result the Social and Liberal Democrats' leader Paddy Ashdown called for SDP members to defect to his party, but this call was not supported by SDP leader David Owen, who instead indicated his party might be prepared to enter into a future coalition government with Labour.