The Green Party believes it is only 73 votes behind Reform in run-up to the Gorton and Denton by-election, HuffPost UK understands.
The party came to that conclusion after more than 13,000 doorstep conversations, according to an internal Green Party WhatsApp group seen by HuffPost UK.
Campaigners in the constituency believe the Greens are now just 0.2% behind Reform, equating to just 73 votes.
The activists described the vote as being on a “literal knife edge”.
But Green activists also used their WhatsApp group to warn they are “seriously short of campaigners for the final stretch of the campaign”.
The party believes that they need 300 people every weekday to campaign across the remaining week, with more 1,000 activists on the trail this weekend and 2,000 people on polling day.
In a message to campaigners, warns that the party is “not even close” to reaching that number right now.
When approached for comment on a potential shortage of campaigners, a party source told HuffPost UK: “That’s campaigns, campaigning. We have hundreds of volunteers out every day and we are expecting Saturday to be the largest action day the party has ever had.
“Our data shows we’re neck and neck with Reform and every extra volunteer out on the streets from now till next Thursday could make the difference to stop Reform.”
Voters in the Greater Manchester seat will head to the ballot box next Thursday for the crunch contest.
The seat has traditionally been Labour so it will be a significant test of Keir Starmer’s authority and approval among the electorate.
The Greens and Reform UK have both soared in popularity over the last 18 months and are hoping to boost their seat numbers in the Commons.
The outsider parties have also insisted they are now locked in a race with each other, while Labour told HuffPost UK that it is only between their party and Reform – with the right-wing group still taking a slight lead.
A Labour campaign source dismissed the Green Party’s data, calling them canvas results which can be manipulated.
“This is a members’ motivation poll,” they said. “It’s nonsense from our perspective.”
The Labour insider said the Greens have a “loud vote but it’s not widespread”.
Meanwhile, the UK Polling Report’s website is currently predicting Labour will hold the seat.
It claimed Labour candidate Angeliki Stogia will win with 35.47% of the vote, while Reform’s Matt Goodwin will come in second place with 29.17%.
The Greens’ Hannah Spencer is expected to come in third with 20.83%, according to the data.
Reform UK has been contacted for comment.