The fans have begged him not to go, but the goalkeeper's mind is made up – and a move to England might just appeal as the Champions League second leg against Manchester City looms

The night Víctor Valdés really took hold of his Barcelona career was the night he let go. May 24, 2006 was destined to be the end; instead it was the beginning, a kind of epiphany. So much so that, asked at the start of this interview if that was the most important moment of his career, he replies: "I would say the most important of my life." He also mentions his three children and his partner but he is talking about the 2006 European Cup final against Arsenal in Paris.

Valdés was 24. "I went into that game knowing the following day I wouldn't be Barcelona's goalkeeper," Valdés says, pulling his plastic chair towards the table. He's been talking for less than 80 seconds and he's already identified the defining moment. Eight years later, he's still here but this season really will be his last: Valdés will depart in June as the best keeper in Barça's history. In May 2006, he won the European Cup. Two more followed, plus four league titles, six in total, two World Club Cups and a record four Zamora trophies as the league's best keeper.

The way Valdés has it, none of that would have been possible without Paris. That night he stopped Thierry Henry twice in the opening five minutes and then again, one-on-one, in the 68th. The then coach Frank Rijkaard described him as "decisive". But what mattered was not just that it changed the minds of others – in fact, Valdés cannot know for sure that it did – but that it changed his.

"The criticism had rained down. No one said anything but intuition told me I was leaving," Valdés explains. "And rather than feeling under pressure, I felt liberated. I just had this idea: sal y disfruta, go out there and enjoy it, because I knew it was my last. But destiny had other ideas, I played well and everything was reconsidered." His mindset, especially. The work remained the same – Valdés talks about being football "mad" and studying strikers because "I don't like being caught by surprise" – but almost by chance he had formulated a new philosophy.

"It's based on how I felt at that moment and how that feeling of liberation could be transferred to every big game from then on. I've perfected the methodology over the years: convincing yourself your reputation's not always on the line: this isn't a constant exam where you're at the mercy of others. Don't be influenced, let it flow. I wasn't really conscious of being under that kind of pressure or that it was affecting me until that night when, suddenly, you go into the biggest game of your career with a totally different mentality and play better than ever. I won the Champions League and a Barcelona career. From that moment, I had a future."

As Valdés talks, eloquently and honesty, it is clear he considers psychology paramount, particularly as a goalkeeper at Barcelona, where the infamous entorno, that maelstrom of politics and pressure, conditions everything. It is also clear that it has not always been easy, or even successful. His contradictions are occasionally compelling. As he puts it: "A year at Barcelona is like two anywhere else."

Valdés paints a picture in which the keeper is an outfield player too, exposed rarely but absolutely: concentration and one-on-ones are their lifeblood. "Our philosophy is to have the ball so the opposition don't shoot often but I can assure you it's not easy," he says. "At times, you're in bits. Mentally it's exhausting. I've finished games where I've hardly touched the ball yet I've got to the dressing room dead. You think: why? Because psychologically you're completely immersed and that can be more tiring than physical exertion."

That at least is the way it used to be. Curiously, this year, his last, is different. On one level Valdés admits he is enjoying the greater workload but in explaining the shift he casts light on the problems Barcelona face, manifest in another defeat on Saturday, their third in the last six league games. "From the start I noticed teams attacking us differently: they're getting to the edge of our area more, taking more shots. It's not all one-on-ones ... and this has been a difficult year with all the off-the-pitch issues too. It's hard for a dressing room to remain hermetically sealed."

A new manager, debate over the style, the Neymar transfer, investigations from the inland revenue, legal charges, a presidential resignation, Valdés's departure, Carles Puyol's too ... this has been an especially traumatic season. But the pressure is permanent.

"The goal at Barcelona does not measure what it measures," Valdés says. "And that's not something you only notice during the 90 minutes. It's everything. Everything's analysed to the last centimetre and if you can't isolate yourself from that, it can affect you. The entorno is vulnerable and marks the dynamic of the club; one day you're up here, the next down here. You think 'what happened?' Barcelona is 'more than a club' for a lot of reasons and that's one of them."

Valdés has felt that pressure especially keenly. He has admitted previously to feeling that doubts always surround him; he has not always enjoyed the warmth given to other players. When one question starts "if I'm not mistaken, this season they're chanting your name for the first time", Valdés's answer begins with: "You're not mistaken ..." When he discusses his Spain call-up, he describes how Vicente del Bosque "put his fingers in his ears and said: 'I'm going to pick this player everyone says is controversial and bad for the squad,'" adding: "I've shown that's not true. My team-mates know I'm not that person."

Does he feel misunderstood, then? "No, no ..." Unknown? "Maybe I've had a greater standing in the dressing room than has been transmitted outside." Does that affect him? "No, because they're like my brothers and they think highly of me. I haven't been aware of all the external criticism; if I had I'd never have survived. Also, the good outweighs the bad, always. Always."

"Ultimately, goalkeepers are on their own," Valdés says. "I like the solitude. I'm passionate about windsurfing: two hours on the water is like a week's holiday, complete disconnection. You see the land a long way off and nobody and nothing can bother you apart from the occasional fish swimming past."

"I'm very ..." There is a pause. Valdés continues: "It might not look like it but I'm quite shy. I'm an introvert. That's the way I am, how I feel. I know my introverted nature has failed me with certain aspects of what this profession demands, like public events, media commitments, galas and so on, but you can't help the way you are."

Now, there is unanimity. Now that he is leaving. For all that he felt Del Bosque had to ignore voices that doubted him, Valdés was just too good not to be called up and he was decisive during World Cup qualification against France. Paris again. Now that they know he is going, they miss him; you don't know what you've got until it's gone. Banners beg him not to go, but his mind is made up. "This year they're chanting my name. I'm proud of that. Maybe it's because they know this is my last season and I'm still giving everything."

Valdés made his debut 14 years ago; 28 years at any other club. At 32, he wants to experience something new; at 32 he has much to offer. He announced a "definitive" decision in January 2013, 18 months before his contract expired and with nowhere, yet, to go. It was unusually bold, brave too and initially it drew media criticism. Fans, though, largely supported him. "I was honest. It's hard for people to understand but I did what my heart told me. People around me have to understand what I am like too. Why hide? Why say 'let's see'?"

So where now? "I've not got anything yet," he says. If the aim is to release the pressure, might Valdés head into a kind of semi-retirement? After his career ends, he admits that the idea of taking a camper van and a surfboard and heading to somewhere "no one knows me" appeals but not yet, and the response is swift: "What's 'retire'? To go somewhere and disrespect my team-mates who want to win and you've got some other attitude? No. Besides, it could be that when you free yourself from certain pressures you optimise your performances."

Valdés does not say England is an option but the idea clearly appeals. He laughs at suggestions he could surf on the Manchester Ship Canal or the Thames; he talks of atmospheres, respect and affection, of "traditions like applauding the opposing keeper"; he talks of "another footballing culture, one I've always identified with"; and he reels off a long list of British stadiums where he's played: from the first trip to Newcastle, to the latest at the Etihad where Barcelona beat Manchester City 2-0 in the first leg of their Champions League last-16 tie, marked by a reunion with an old friend and a certain familiarity of approach.

'I didn't see Txiki [Begiristain, director of football] in Manchester, but it was great to see Yaya [Touré]. He brought seven mates on to the team bus and we were there for two hours taking photos, as if he was still in the team. It can be sad when people move on and you know you won't see them tomorrow after everything you shared, but you get used to it. You stay in touch too: this Christmas I saw Thierry Henry in New York."

"Yaya started off as a holding midfielder here and we used him a lot as a central defender but his strength is carrying the ball forward. A league like the Premier which is more open helps. He protects the ball well and now you're discovering something I already knew very well: that he has a very good shot."

Not that there was much evidence of that in the first leg. "Some might think City ceded the ball to us, but I look at it as Barcelona playing well," Valdés says, now with eyes firmly on Wednesday's return leg at the Camp Nou. "I don't think the tie's over; 2-0 is a good result but not definitive, especially with the talent they have. And [Sergio] Agüero will be back. He scored goals against me at Atlético and he's a spectacular player: he gets shots away quickly and moves intelligently. They're an equipazo, a great team. We have to play well or it'll cost us."

Recent results have left Barcelona wobbling and the sense of an era ending lingers. For Valdés, that is inevitable. The question is how it will end. They are, after all, well placed to reach the quarter-finals of the tournament that Valdés admits most excites him and most marked him. In 2006, he thought the European Cup final was going to be his last game for Barcelona; eight years on, he hopes it will be. If Barcelona were to reach Lisbon on 10 May and prevail there, it would be his fourth European Cup final win. That is something Valdés did not know, but it would be more than any goalkeeper in history. And it all started in Paris.

The ups:

• Has a cabinet full of silverware: 6 La Liga titles, 2 Copa del Rey titles, 6 Supercopa de Espana titles, 3 Champions League titles, 1 Super Cup, 2 Club World Cup titles. Not to mention World Cup and European Championship medals

• Has won the Ricardo Zamora trophy five times, given to the goalkeeper with the lowest goals-to-games ratio in La Liga

• Made his 10th penalty save for Barcelona in all competitions, during their 4-0 victory against Ajax this season

The downs

• Was not picked for Spain until 2010, was an unused substitute in the World Cup and has managed only 13 caps.

• Suspended for four games last season following an aggressive confrontation with referee Miguel Angel Perez Lasa after the final whistle in their 2-1 defeat to Real Madrid.

• Handed bottom club Espanyol their first victory at Camp Nou in 27 years, breaking a 14 game winless streak, in 2009 after he cleared the ball straight to Iván De La Peña, who sent a sublime chip over Valdes's head

Additional reporting: Samar Maguire