Over the last few days I’ve been giving a few talks explaining why we should treat the polls with caution. If you look only at the latest polls then the outcome of the election appears fairly certain. Ever since a majority of MPs voted to hold the election the incumbent Conservative Party has averaged 38%, the Labour Party 27%, the Liberal Democrats 16%, Brexit Party 10%, Greens 4% and Scottish National Party 3%. Prime Minister Johnson and his party continue to average an 11-point lead which, if this holds, would likely deliver a comfortable majority. Prime Minister Johnson can also point to other favourable metrics. When voters are asked who would make the ‘best Prime Minister’, a clear plurality (43%) say Johnson while only a small minority (20%) choose the Labour leader, Jeremy Corbyn. It’s worth noting that working-class voters break strongly for Johnson (48%) over Corbyn (18%), as do voters in the Midlands and Wales (48% to 15%) and the North (41% to 20%), areas that cover the ‘Red Wall’ that Johnson is targeting. In terms of issues, the polls also suggest that, on the whole, voters are more trusting of Johnson than Corbyn to deal with Brexit, the economy and crime, while Corbyn only leads on health. Crucially, perhaps, when it comes to leadership ratings Johnson is also backed by a clear majority of Brexit Party voters (80% back Johnson) and Leavers (73% to 5%). However, the party system remains very fragmented. Combined, at the start of the campaign, the two main parties hold only 61 per cent of the vote which is well down on the 80 per cent polled in 2017. Labour is weakened by the fact that it is only attracting 57 per cent of its 2017 electorate. A large number of these voters (18%) have decamped to the Liberal Democrats while 16% have switched to the Conservative Party or Brexit Party. Remainers are still more divided than Leavers. The Remain camp is divided 36% Labour, 33% Liberal Democrat, 17% Conservative and 6% each for the SNP and the Greens. Leave breaks far more strongly in one direction, with 59% planning to vote Conservative and 22% planning to vote for the Brexit Party. If Johnson continues to squeeze the Brexit Party vote, his job will become easier. But there remains considerable volatility all round and there are good reasons to expect further change during the campaign. This brings us to the question of how might Nigel Farage and the Brexit Party impact upon the Conservative Party’s fortunes? If you look only at the polls that have been conducted at the start of the campaign then – assuming these hold – the Conservatives could quite plausibly expect to win 357 seats and a comfortable majority. But what might happen if the Brexit Party runs hundreds of candidates and is successful at attracting disillusioned Conservatives who might not like Johnson’s Brexit deal? The chart above shows how our baseline picture changes as the Brexit Party eats into 1% to 6% of the Conservative vote. While holding other things equal, this suggests that Johnson and the Conservative Party could withstand a 1-3% loss and still win a working majority with 337 seats. But beyond this things become more difficult. Losing 4% of their vote to Farage reduces the total number of Conservative seats to 331 and leaves them with a very thin majority. With a 6% loss to the Brexit Party the Conservatives fall to 320 seats, very similar to the 317 seats Theresa May won in 2017. Jeremy Corbyn and Labour might not match their spectacular surge of 2017 but even a modest upward trend in their support would also hurt Johnson and the Conservatives. This, in turn, means that even a small defection of Conservative voters to the Brexit Party, especially if it occurs in the Midlands and North, would pose a real threat to Conservative hopes of a majority. The bottom line is that the Conservatives need as many Brexit Party supporters as possible. If they get them, then they will likely win a comfortable and possibly large majority. However, if things go the other way – if Farage has a good campaign and Conservatives start to flow the other way to the Brexit Party – then the chance of Boris getting his cherished majority are sharply reduced. There is all to play for.