It was held after the incumbent Conservative MP Peter Smithers was appointed as the Secretary-General of the Council of Europe.
The by-election was one of four (the others being Bury St Edmunds, Devizes and Rutherglen being held on the same day in which the seat was being defended by a candidate supporting the incumbent Conservative government.
[3] The Conservatives lost Rutherglen, but held Bury St Edmund's, the last of the seats to declare, with what was reported by The Glasgow Herald to be a smaller swing against them than expected.
The same newspaper noted that while the four results gave a mixed picture, with Winchester seeing the biggest swing against the Conservatives, overall they cast doubt on opinion polls suggesting a significant national Labour lead and perhaps would give Harold Wilson "the first faint incredulous thoughts" that he might not prevail at the coming general election.
[4] This article about a by-election to the Parliament of the United Kingdom in England is a stub.