A grey single-breasted jacket, a black cardigan and a neat white shirt: Philipp Lahm made a point of dressing up for the mother of all dressing-downs in November 2009. The Bayern Munich captain had been ordered to meet the board of directors after giving an unauthorised interview to Süddeutsche Zeitung that read like a Bavarian version of J'accuse. In a wide-ranging attack on the club's culture of short-termism and their haphazard transfer policy, Lahm deplored the lack of a comprehensive "playing philosophy" and warned that recruits were simply being bought "because they were good players" with scant regard for the squad's actual needs.

After meeting his irate superiors at Säbener Strasse headquarters – getting on the wrong side of Uli Hoeness, the general manager, and Karl-Heinz Rummenigge, then the vice-president, is not for the faint-hearted – the full-back was fined a record €10,000. "We are disappointed," Rummenigge, now CEO, said. "He's violated internal regulations in a glaring and inexcusable manner."

Yet the player's critique was met with approval by the supporters. Lahm had touched a raw nerve. The interview brought Bayern's lack of direction in the transfer market into sharp focus and helped to strengthen the hand of the then manager Louis van Gaal, who was close to getting fired that autumn.

The Dutchman's bloody-mindedness and willful neglect of the defensive side of the game made his dismissal inevitable 13 months ago. But his tactical groundwork and courageous promotion of youth team players such as the centre-back Holger Badstuber, the left-back David Alaba (both suspended for the game against Chelsea) and Thomas Müller have underpinned Bayern's renaissance.

Without Lahm's intervention, Van Gaal would not have been able to "leave his mark on the team and give us a system", as he puts it, and in turn the German record title holders would have been extremely unlikely to reach Saturday's Champions League final, their second in three seasons. "We have been able to develop as a team," Lahm says, with a hint of pride. "We now have a core and a playing philosophy, and the club has bought the players that fit perfectly. We're continually improving and the results have shown that we're on the right path." The €10,000 fine now looks like money well spent.

Lahm was well placed to speak out. He grew up in the Munich suburb of Gern, 10 minutes by car from Bayern's former home, the Olympic Stadium. He joined Bayern as an 11-year-old and was systematically versed in the club's mia san mia (we are who we are) ideology, an unshakeable belief in their own greatness and almost impossible ambition: at Säbener Strasse, second best is a disgrace. "You get told at a very young age that only winning is acceptable," explains Lahm, "but also that playing for Bayern comes with a lot of responsibility. You are representing the club and have to behave accordingly."

At the time he explained his whistle-blowing as the action of a worried "home-grown player who had Bayern at [his] heart". But one could also detect an element of more personal concern. Lahm, who had turned down an offer from Barcelona against the advice of his agent that summer, was getting worried that the loyalty to his home-town club was stifling his own progress. As the best German full-back since the World Cup-winner Andreas Brehme, he was beginning to feel both under-valued and over-qualified at a club that was underachieving, relative to its financial power, since winning the Champions League in 2001.

The chance to lead his men out on Saturday has vindicated his decision to speak out and stick around, however. Lahm is full of praise for a side that outplayed Real Madrid in the semi-final ("that's when we realised that we are at the same level as the very best in the world") and that has found a sense of tactical maturity and balance under the 66-year-old Jupp Heynckes. "He's rectified Van Gaal's mistakes," says Lahm. "We are less static in possession, more flexible, we have a much better mix between attack and defence and everyone's working hard all over the pitch."

Lahm praises Arjen Robben and Franck Ribéry in that respect, "two fantastic individualists" who have visibly curbed their selfish instincts to track back more in recent weeks – even if the wingers argue about the right to take free-kicks at times. He is also full of admiration for Mario Gomez, "a real, true striker", acknowledges the development of Bastian Schweinsteiger into a world-class central midfielder and lauds the contrasting talents of Toni Kroos ("great passer, wonderful technique") and Müller ("always on the run, great eye for goal"). "We have all been able to grow together, we're much, much better than two years ago. We can feel it, there's a belief now. The confidence is much, much higher than before the 2010 final [against José Mourinho's Internazionale in Madrid]," he says.

Playing at home will be only "a small advantage," he adds, since nearly half the stadium will turn blue on this occasion. He is also full of respect for the opponents. "Chelsea are incredibly experienced. We all watched the Barcelona semi-final and the way they fought tirelessly and defended for each other was hugely impressive. They have togetherness. And I'm sure they will be really up for it. At 28, I'm one of the older guys in my team, we might get another shot at the trophy. But many of their key players are around 30 or older. It could be now or never for them. That's a very dangerous situation."

Rummenigge has compared Roberto Di Matteo's side to the ever so slightly over-the-hill Bayern side of 1975 and 1976 who won two more European Cups after their initial 1974 triumph by sheer force of will. "We played some pretty bad stuff in the league," the former West Germany striker says. "But in the important matches and in the finals, we pulled together in incredible fashion. It was if there were two teams."

After the initial euphoria about Bayern's passage to the final – and Barcelona's absence from it – Chelsea are being increasingly seen as a very tough proposition. "They're a bit like protagonists in a Sam Peckinpah Western," wrote Süddeutsche, the local broadsheet: "Men who know they have no future are capable of anything."

That Chelsea will be without the suspended John Terry will not matter that much, Lahm thinks. "They might miss his experience a little but they've got superb players who can come in for him."

To ramp up the atmosphere, Bayern have hung 500 "one city, one dream" posters. In addition to the 63,000 at the Allianz Arena, another 90,000 fans have bought tickets for two public viewing events. "I trust my home town to get behind us," Lahm says, even if he will not be hanging a flag from his own balcony. "I'll be there, wearing red in the stadium, instead," he says with a laugh. "Hopefully, I can do my bit that way."