Winning a recent by-election has raised the hopes of Conservative, Liberal Democrat and Labour campaigners, but does not foretell what will happen in a general election. To paraphrase Aristotle's saying about swallows, one by-election does not a general election victory make. When 650 seats and control of government are at stake, at least two parties are bound to be losers.
Nationwide opinion polls show that if a general election had been held in July, the Tories would have been certain losers. Poll support for the Conservatives averaged just under 27 percent nationally, 18 percent below the level of support the party won at the Uxbridge by-election. The most likely outcome would have been a Conservative loss of almost 250 seats. On this basis, there is only a one percent probability that the party would emerge with the most MPs at the next general election. Even then, the Tories would still be short of the absolute majority needed to keep control of Downing Street.
The Liberal Democrats' by-election vote showed that their strategy of selectively targeting seats is working. It won Somerton and Frome with a 28 percent increase in its vote, while the vote of its candidate in Uxbridge fell by four percent and in Selby and Ainsty the party finished sixth with three percent of the vote.
Nationwide polls confirm the success of selectively targeting a limited number of seats. In July its nationwide share of the vote is down one percent from the last general election. However, while its vote was down in a majority of constituencies, it is up in target seats. On this basis the Liberal Democrats would be likely to win 22 seats if a general election were held today and have an outside chance of winning as many as 40 seats.
Nationally, July opinion polls show that the Labour Party remains almost 19 percent ahead of the Conservatives, a lead sufficient to give it as many as 463 MPs at a general election. Both Conservative and Labour campaigners agree that Labour's failure to translate its nationwide lead into a by-election victory in Uxbridge was due to the Tories concentrating on the plan of the Labour mayor of London to introduce a £12.50 tax on local motorists' daily use of highly polluting cars. Even though the issue was local, it reflects a nationwide debate about the cost to the electorate of anti-pollution measures.
Rishi Sunak is now launching a campaign to win back lapsed Tory supporters by stressing that the Tory policy on climate change will protect voters' pocketbooks as well as the climate, while Labour will spend tens of billions of pounds of taxpayers' money on anti-pollution policies.
To be forewarned is to be forearmed. Sir Keir Starmer had already been alerted to the cost of its green policies by unions fearing they would threaten their members in the energy industry losing their jobs. The Uxbridge defeat underlines that warning. Given Labour's massive lead, Starmer can afford to lose a few votes to the Green Party and face down Ed Miliband, his shadow Energy Secretary, and Sadiq Khan. What Starmer cannot afford to do is give the Conservatives an issue it can use to deprive Labour of an absolute majority at the next general election.
Richard Rose is Britain's senior psephologist and an expert on party government. His new book 'How Sick is British Democracy?: a Clinical Analysis' is published by Palgrave.