LONDON — Even the smoothest election campaigns can fall flat over a policy snafu.

In the U.K.'s 2017 campaign, the 88-page Tory manifesto tanked Theresa May's race, despite the former prime minister being on course for a comfortable victory before its publication. By contrast, the Labour manifesto, which was leaked to the press, gave its leader, Jeremy Corbyn, a boost as his policy platform proved unexpectedly popular.

In the run-up to this year's December 12 vote, the Conservatives played it safe, with a shorter manifesto of just 59 pages and few surprises. Their policy document contains nothing as remotely controversial as May’s so-called “dementia tax” to tackle the social care crisis.

Boris Johnson’s main pledge is delivering Brexit by January 31 to restore trust in politics and focus on “the people’s priorities” — the NHS, schools and the police, all of which faced severe cuts under the previous Conservative-led governments. The Tories also ruled out extending the Brexit transition period — currently due to end in December 2020 — which strengthens Johnson's commitment to pulling the U.K. out of the European Union but leaves very little time to negotiate a new arrangement with his country's largest trading partner.

In another move designed to appeal to voters who backed Leave in the U.K.'s 2016 referendum, the Conservatives have promised to decrease net migration, but without committing to a figure.

Labour, meanwhile, doubled-down on their plan from the last election, which was widely seen as the most left-wing policy program by a British party in a generation. Their manifesto, which runs to 107 pages, was pitched as a “radical plan” to transform Britain by tackling inequality, protecting the environment and reversing cuts.

Corbyn is trying to galvanize support from both Leavers and Remainers by promising to get a new Brexit deal — of a softer type than Johnson’s — in just three months, and offer the public a chance to choose between that deal and remaining in the EU in a second referendum.

Meanwhile, the Liberal Democrats have sought middle ground when it comes to spending on public services. Their pledge to stop Brexit immediately after the election if they win a majority could backfire if voters buy Labour’s argument that Brexit cannot be canceled without a second referendum.

Although all three party manifestos present a view of the U.K. as a country that would protect the environment and its public services, the three propose very different levels of public spending. The Tories restrained program pledges to just £2.9 billion extra a year by the end of the next parliament, whereas Labour promises an extra £83 billion a year. The Liberal Democrats plan to spend an extra £50 billion a year over the same period.

Here are all three documents compared across key policy areas:

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