The St Marylebone by-election of 22 October 1970 was held after Conservative Member of Parliament (MP) Quintin Hogg became a life peer. The seat was retained for the Conservatives by Kenneth Baker, who had lost his previous seat of Acton at the general election four months earlier; Baker would go on to represent the Mole Valley seat in Surrey and become a long-serving Cabinet minister.
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Constituency of St Marylebone (UK Parliament constituency) | |||||||||||||||||||||||||||||
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 A map of parliamentary constituencies within the County of London at the time of the by-election, with St Marylebone highlighted in red. | |||||||||||||||||||||||||||||
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| Party | Candidate | Votes | % | ±% | |
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| Conservative | Kenneth Baker | 10,684 | 63.49 | +1.40 | |
| Labour | Keith Morrell | 4,542 | 26.99 | -2.32 | |
| Liberal | Michael Vann | 1,038 | 6.19 | -2.41 | |
| National Front | Malcolm Skeggs | 401 | 2.38 | New | |
| Fourth World Group | John Papworth | 163 | 0.97 | New | |
| Majority | 6,142 | 36.5 | +3.7 | ||
| Turnout | 16,828 | ||||
| Conservative hold | Swing | ||||
