IN THE build-up to Britain’s election campaign period it seemed the Conservatives were destined to be the stronger of the two main parties in the “air war”, what with their more popular leader, their more experienced front-bench, their clearer messages, their stronger rebuttal operation, their better-disciplined campaign and their oodles of cash. It also seemed clear that Labour would win the “ground war”.

Yet three weeks into the the campaign, many are reaching the conclusion that the Tory “air war” advantage is smaller than had been expected. Some of David Cameron’s public appearances have been lacklustre or irritable, while Ed Miliband has outperformed rock-bottom expectations of him (“Where did the weird guy go?” asks Carl Dinnen of ITV News). In the Sunday Times today Peter Kellner, a pollster not known for sugar-coating his advice to Labour, writes: “voters are warming to the idea of an Ed Miliband-led government” and “the Tories are currently losing both the air war and the ground war.” He lists various worrying details for the Conservatives: “many more people told us they had noticed something negative about the Tories than anything positive”, “the Tories have failed to persuade voters that theirs is the party for ‘hard-working families’” and—perhaps most troublingly, as they regarded the Labour leader as their secret weapon—“Miliband’s personal rating has climbed to his best level for more than two years”.

Far from the media scrums and the television cameras, however, another, less-discussed story is emerging that is making Labour types just as chipper. Just as the Tory strength in the air war is surprisingly lacking, Labour’s advantage on the ground is proving greater than expected. The Conservatives have put significant efforts into bolstering their local campaigns: parachuting in American-style organisers, sending hundreds of young activists out to marginals (an operation known in the party as the “shag bus”), and generally trying to make doorstep campaigning more fun. There were good reasons to believe this would work: Grant Shapps, the party chairman, has an excellent reputation as a ground campaigner in his Welwyn Garden City seat, and pulled off a strong win in the Newark by-election last year, when he pioneered techniques that he is now deploying nationally.

Yet poll after poll shows that they are insufficient. Lord Ashcroft’s surveys of Labour-Tory marginals paint a picture of overwhelming Labour supremacy on the ground. In every single one of ten seats in the latest batch (see Lord Ashcroft’s chart, below), more voters had received contact—be it a leaflet, a phone call or a canvassing visit—from Labour than from the Conservatives. In some the gap was huge: 34% to 60% in Finchley and Golders Green, for example, and 43% to 74% in Milton Keynes South. The same was true of the previous ten marginals polled by the peer. Overall, in these twenty constituencies, the Tories had contacted 53% of voters; Labour had contacted 68%. That finding is echoed by Mr Kellner today, who writes: “YouGov research finds that up to Friday, Labour had contacted more voters locally than the Tories, in person, by phone, via leaflets and by email.”

Even Labour insiders are surprised at the size of the gap. A regularly updated chart on the wall of the party’s headquarters at Brewer’s Green, near Victoria station in London, monitors the rate at which activists out in the country are making contacts (crucial not just to winning over voters but also to the get-out-the-vote operation on election day). This is how it currently looks (the spikes are weekends, when the most intense campaigning takes place):

The dotted green line on the chart shows the target for cumulative contacts, the solid green one the actual number. The latter is about to hit the 3m mark (corresponding to about 8m knocked-on doors) over a week ahead of schedule. Labour is now routinely making more than 75,000 contacts per day. Why the advantage? The difference in size, age and tribalism of the two parties undoubtedly plays a part. The Conservative Party has about 150,000 members. The average one is about 68. Just 17% of members are aged between 18 and 39. Constituency associations are relatively independent from the central party. Labour has about 200,000 members. It is markedly younger (estimates of average age put it around 50) and has a more unified structure. Other explanations concern strategy and process. Labour’s campaigning infrastructure has been overhauled over the past five years in a way that the Conservative one has not. Under Iain McNicol, the party’s general secretary, it has been drastically decentralised: the central office in London has been slimmed down and the number of staff posted to the regions has risen from around 100 to 300. The party has invested in online fundraising; which brought in £140,000 in the 2010 campaign but has already garnered over £2m in the current race. It selected candidates and hired organisers earlier than in the past, giving them time to gradually build up local campaigns. Mr McNicol also brought over Arnie Graf, an American campaigner who devised the methods behind Barack Obama’s movement-like presidential campaign in 2008, to train activists. Mr Graf’s “community organising” approach involves building election-fighting capacity in advance by running campaigns on local issues, from low pay to litter in the streets. Notably, one of the local Labour parties that has most enthusiastically embraced it, Southampton Itchen, has one of the best showings in Lord Ashcroft’s poll in March, turning a neck-and-neck projection last August into an eight-point lead over the Conservative candidate—who, according to the poll, had contacted four voters for every five reached by Labour.

All this should worry Conservatives. Their so-so national campaign can be pepped up. Mr Cameron’s appearance on the Marr show this morning was stronger than some of his previous outings; fierily defensive of his pledges to boost child care and give social housing tenants a hand up. The Tories have further counter-intuitive interventions planned for the coming week, and the prime minister is said to be preparing furiously for the final televised “debate”, a special edition of Question Time on April 30th. Yet at this late stage there is little they can do about their local campaigning weaknesses. Recruiting new members and building election-fighting capacity takes months and years, not days and weeks. If the Conservatives end up out of power after the election (a far-from-certain prospect, albeit one that looks more possible than three weeks ago), they will need to rebuild from the ground up.