A gauge of how Harborough Town’s history-making run to the second round of the FA Cup has captured so many hearts is perhaps best illustrated by the assistant manager and his 11-year-old spaniel, Martha. “I walk my dog every day and never before have people stopped me to say: ‘Well done on your progress,’” David Staff says. On Sunday the lowest-ranked team left in the competition, 15th in the Southern League Premier Central, the seventh tier, will be backed at Reading by almost 3,500 supporters, about 15% of the Leicestershire market town. “Because I’m enjoying the attention, she’s getting more walks than ever,” he says, breaking into laughter.

The last time Staff received such acclaim was when he conquered the travelator to win the reboot of the TV show Gladiators, from which he has fond memories and a few mementos. “Doom broke my nose in an event,” he says. “After I won, the next morning we were all having breakfast with Wolf at the hotel near Shepperton Studios. I’ve got a couple of foam fingers in the loft, my leotard is up on the wall and the ‘G’ trophy in my office. I don’t put it on work calls because I think it’s a bit too much – I try to hide it at the bottom of the frame.”

It is approaching 8pm and before running the squad through the plan for the next hour of training, Staff, who has lived in Market Harborough his entire life, is well-placed to discuss how interest has snowballed. “The Amazon driver is saying: ‘Good luck at the weekend.’ When we scored against Tonbridge [in the first round], I didn’t want to be in the dugout, I wanted to be in the stand. I saw friends from school: Jimmy Burton, who supported us when 50 people were here.” The queue from the foyer to the bar for the final 500 tickets is another giveaway. Some things never change, though: the co-chairman Peter Dougan will lay out the kit in the away dressing room, as he always does.

Here, at the club’s stadium on the edge of town, there are cupcakes in the home changing room to celebrate the goalkeeper Elliott Taylor’s 27th birthday. The roulette wheel of fortune spins on the massage table, determining the next wave of punishments. Taylor, a landscape gardener whose days sometimes start before 5am, embodies a squad that includes bricklayers, project managers, finance brokers, a care worker and a gas fitter. The manager, Mitch Austin, runs a fibre optics company. “We’ve got an intelligent back four,” says Staff, who works in healthcare. Some players will work on Saturday before travelling south and staying overnight before the game.

Harborough, who usually train twice a week, almost didn’t get past the first qualifying round, fighting back from 2-0 down in a replay at eighth-tier Darlaston Town to win 3-2 courtesy of a 97th-minute penalty. In the clubhouse, which doubles up as the boardroom, players make a beeline for Dougan, whose association with the club goes back to 1986. He has played for the men’s, veterans and walking football teams. “Chairman, are we getting the tickets today?” asks the midfielder Ben Starkie. “Because you’ve paid, yes,” replies Dougan, smiling, as he sifts through the 685 tickets players have bought for friends and family.

Austin and Staff, a yin-yang pairing by their own admission, spent Tuesday night at Oakwell taking in Reading’s draw at Barnsley. “We have a desire to be the best we can but also we cannot be too deluded, so we have to understand who we are and they are, the gap, but try and create more dreams,” says Austin. The amount of video of Reading has helped Harborough do their homework but Taylor has employed another tactic. “I go on Fifa [the video game] to get information, players’ heights – it is quite useful to have a look.”

This run has generated about £140,000 for a club powered by volunteers, including Laurence Jones, the chief executive. “It’s a game-changer for a grassroots club,” says Dougan. Since Austin, previously assistant at St Ives Town, took charge four years ago he has won two promotions, the second in May, and there has been a seven-fold increase in attendances. “I’ve come from the bottom,” says the 36-year-old of his coaching journey. “You can’t go any lower than I was: games without linesmen, at Woodford United. I was the third-team manager at Bugbrooke St Michaels … it was the best job in the world.”

The cup run has turned players and staff into local celebrities. Last weekend Austin switched on the Christmas lights in the town. As per Football Association regulations, this week the club held a pre-match press conference. The trip to Reading, the captain Ben Williams says, is the talk of the town, everywhere from his child’s nursery to his barbers. “Dean Rushby, the head steward here, a taxi driver, picked up an 80-year-old lady the other week and she said: ‘Harborough Town, aren’t they doing well?’” says Dougan.

Williams, also a Harborough lad, is the longest-serving player after a dozen years on the books. “Life sentence,” he grins. “I was here when it was a grass pitch and 40 fans.” Now their base comprises two artificial pitches and nine grass pitches, home to 65 teams, from under-fives to disability and girls’ teams. Every weekend more than 900 kids represent Harborough. “On Sundays, we can have 25 youth matches here,” Jones says proudly. “It used to be a three-sided pitch on a hill … there was more grass off the pitch than on it. Now this place is in use seven days a week, a thriving community club. We touch a lot of people’s lives in this town.”

Harborough have Bermuda and Tanzania internationals in Jutorre Burgess and Starkie respectively, the latter kicking off the calendar year against Egypt and Mohamed Salah in a warmup game for the Africa Cup of Nations in Cairo. Then there is Sandro, a shock signing this month. “I didn’t expect it, but I don’t mind it,” smiles Starkie. “If fit and he can pass the ball five yards, the beast will be playing,” Austin says of handing the former Tottenham midfielder a debut. “Match fitness, he’s lacking, but we’re talking a 17-cap Brazil international.”

The story goes that Austin, a Spurs season-ticket holder, floated the idea after meeting the 35-year-old, who is based in Portugal and joined his teammates at training for the first time on Wednesday, in a hospitality box at the north London derby in September. There are “Sandro 30” shirts for sale in the club shop. Rosie Ford, the club’s diversity and inclusion champion who will be on one of the 14 supporters’ coaches bound for Reading, tells of her joy at getting a selfie with Sandro. “We thought: ‘There’s no way he’s going to send a copy of his passport, national insurance,’ but he did,” says Dougan. “He’s had nothing off us; he paid for two Harborough Town shirts for his boys. It’s crazy.”

The journey to this point has seen Harborough overcome Darlaston, Stourbridge, Leamington and the two-time winners Bury. For Ford, the Reading match means everything. “If the boys win, it will be the proudest day of my life,” she says. As the players bring in the goal nets and the coaches head inside, Austin ribs Staff, mimicking the former Gladiators referee John Anderson. “Three! Two! One!” he shouts. For Harborough, it is almost showtime. “Some of the chaps were cramping up after 75 minutes at Tonbridge; what’s it going to be like at Reading?” says Staff.

Austin cites Maidstone’s unlikely fourth-round triumph over Ipswich in January, when the sixth-tier side upset a team 98 places above them and en route to the Premier League, as inspiration. Harborough sit 89 places below Reading. “In the first 10 minutes of that game Ipswich hit the post twice, then the bar, and it looked like it was going to be 10-0 Ipswich,” Austin says. “And then Maidstone went and won 2-1, scoring with their only two shots. It can happen. Can it be us? We hope so. Can Reading have an off-day? I hope so. Can Harborough have the best day of our lives? I hope so.”