We’re off, and Labour has it all to do. The Conservatives start the campaign with a 10-point poll lead, a margin that translates into an overall majority of about 58 for Boris Johnson, according to estimates produced by Electoral Calculus.

If anything, the latest Brexit wrangling has benefited the Conservatives, extending the party’s lead by two points since 1 October, even as it became increasingly clear that Johnson’s “do or die” Halloween deadline would be missed.

Certainly, the Conservative strategy for an election campaign looks simple enough – “let’s get Brexit done” – an appeal that plays to the idea that the nation is worn out by Westminster’s endless battles.

That contrasts with the opposition’s argument, easy to portray as overly complex: vote Labour, negotiate a new deal and have referendum on the deal the party just negotiated. It is a promise of more Brexit debate and no certain final outcome.

Labour’s best hope is to reset the agenda, if it can convince the electorate that Brexit is not so important. It worked in 2017, largely because voters thought the UK’s exit was a foregone conclusion, but will be harder this time around.

Ipsos Mori polling suggests that, after months of arguing in Westminster, around half the electorate think Brexit is the most important issue facing the country. Next is the NHS at under 10%.

In a campaign, the opposition knows it can draw on a suite of policies beyond where the Conservatives can go: renationalisation, free student education, tax increases for wealthy earners and perhaps on public spending, although here Johnson has tried to blunt the anti-austerity attack with pledges on schools spending and police numbers.

Labour is way ahead among those aged 18 to 34, where student finance looms large, according to Ipsos Mori, although that is more than offset by a clear Conservative lead among the over 55s and a marginal lead among 35- to 54-year-olds. Pledges made to pensioners and older working age voters by both sides will be critical – particularly after the Tory disaster of the dementia tax in 2017.

Meanwhile, the Liberal Democrats are ahead of Labour among middle aged voters and nearly level pegging with the over 55s. But Jo Swinson’s party will need to establish itself quickly in the campaign to avoid being squeezed. Already the anti-Brexit party has lost two points in October, from 20% to 18%.

That would, however, amount to an 11 point gain from the Lib Dems’ dismal showing in 2017 and an extra 18 seats on an even swing. But, barring something unforeseen, it remains hard to see how they can win significantly more than 30 seats, up from 12 last time.

For Johnson, margins are finer still. If the Tories lose all its 13 seats in Scotland to the Scottish National party – a distinct possibility given the polling there – it needs to gain 21 to get to an overall majority of 326. Other Tory seats in London and, to a lesser extent south-west England, could be at risk, too.

Twenty one may sound a lot to pick up as a minimum, but that could be achieved with a modest swing from Labour and the Lib Dems of just 1.4%. On the other hand, a swing away from just the Tories to Labour of 1.97% would make Corbyn’s party the largest at Westminster with 291 seats.

Labour can win an overall majority if it gains 64 seats from its 2017 result of 262. That would need a 3.6% swing from the Tories, Plaid and the SNP. But, crucially, without gaining a single vote in Scotland, Corbyn would require a more significant swing – 5.9%. That would be a memorable result, not least because it would mean Labour snatching Johnson’s own seat of Uxbridge.