Since the general election, the Green Party of England and Wales’s performance in council by-elections has not been particularly impressive. For example, in by-elections held between September 2015 and September 2016, the party’s average vote share was down 3%, according to Britain Elects.

The most obvious reason for this is that Jeremy Corbyn has stolen the Greens’ left-wing thunder. Many former Green members are among the hundreds of thousands who have joined the Labour Party since Corbyn first ran for the Labour leadership so it makes sense that many Green voters will have gone the same way in by-elections.

Looking closer at by-election results seems to back this up. Labour’s average council by-election vote share decreased by 2% between September 2015 and September 2016 but, in seats where the Greens have done well over the past decade, the Labour party’s vote share generally increased after Corbyn was elected.

These seats are usually urban Labour strongholds, with lots of young and university-educated people. Places like St Ann’s in Haringey (North London), where Labour were up 12% and Greens down 3%; East Brighton, where Labour were up 11% with the Greens down 9% and Hackney Central, where Labour were up 11% and Greens down 13%.

However, according to several people involved in by-election campaigns, it’s not as simple as it seems. Benali Hamdache, the election coordinator of Islington Greens, said: “The main caveat is that we’ve always done terribly in by-elections, it’s just that people are noticing now. It would be interesting to see a figure for average vote share lost for each year since 2008. My guess is that it’s not as dramatic as people think, with regard to Corbyn.”

According to Hamdache, the issue is that the Greens can’t match the other parties’ manpower and resources in by-elections. In one of the most recent by-elections, for example, Labour had 400 people getting the vote out on Election Day while the Greens had just five. Samir Jeraj, who recently ran for Mayor of Hackney and came second to Labour, agreed. “Mainly it’s down to other factors [than Corbyn],” he said, “Corbyn was more of a factor in the London [Mayoral and London Assembly] elections. We’re usually out-campaigned in by-elections.”

Another reason for Greens performing badly in by-elections is that postal votes are over-represented in by-elections. As postal voters are disproportionately older, and Green voters are disproportionately younger, this works against the party.

However, there have been exceptions to this by-election rule, and these exceptions may point to how Greens can thrive. The most spectacular exception was in the ward of Gypsy Hill, a fairly average neighbourhood in the borough of Lambeth, South London. Here, the Greens went from 11% to 42% while Labour went down from 66% to 43%, according to Britain Elects. The reason for this was that Labour’s local candidate was a member of the Blairite ‘Progress’ group, and the local Labour Party had angered locals by cutting funding to libraries and suspending a Labour councillor who protested.

A similar situation occurred in Forest Gate North where, although the candidate was a Corbynite, Newham Council and Newham’s Labour Mayor, have developed a reputation for patronising and attacking local campaign groups like the E15 Mums’ campaign for social housing. In a July 2016 by-election, Labour’s vote went down from 58% to 53% whereas the Greens went up from 14% to 31%.

Thankfully, Labour councils aren’t this bad everywhere but where they are, a well-run campaign such as that run (by now co-leader Jonathan Bartley) in Gipsy Hill could be effective. According to Rob Telford, a Bristol activist who recently ran for the party’s national elections coordinator: “The solution is to be better organised and actively point out where local Labour have not been progressive, which it’s usually not too hard to find.”

So while some Green supporters advocate responding to Corbyn with a disastrous rightward lurch to the ‘centre ground’ (which the public won’t notice and party members will hate), the real solution lies in fighting Labour on a local level and in running effective, well-organised campaigns.