The director of One Direction's new documentary has revealed that, although the band agreed to give him access to everything he wanted, there were moments when the boys were "vulnerable" and he decided himself to stop filming.

"When you're somebody in the position that they're in, there is a kind of vulnerability all the time," Morgan Spurlock tells HuffPostUK.

one direction
Morgan Spurlock (centre) with One Direction, whom he's spent the past year filming

"We filmed in moments when they were sad, when it was hard, when they didn't want to talk, but we got them to... but there are times when you say, 'Ok, now we should stop, now's a time when someone needs their space.'"

Spurlock may seem an unlikely choice to document 'This Is Us', an undiluted celebration of globalised pop. His previous films demonstrate an eyebrow permanently raised to such corporate endeavours, including force-feeding himself with hamburgers ('Supersize Me') and approaching corporations to sponsor his film on product placement ('The Greatest Movie Ever Sold').

It seems even he couldn't resist the chance to get inside the bubble of what has been described as Beatlemania all over again.

"This wave of popularity and dedication...," Spurlock smacks his forehead. "I've seen fans of bands, but this is the closest to Beatlemania I've seen in my life."

morgan spurlock
Morgan Spurlock was previously best known for force-feeding himself hamburgers for 'Supersize Me'

He cheerily agrees that more people will see One Direction's 'This Is Us' than all the rest of his films put together, but he still had the confidence to push for full access to Zayn, Niall, Louis, Liam and Harry, something to which all five readily agreed.

"They said, we want fans to see what it's really like to be... us. They put that trust in me, which was great.

"The surprising thing for me is the guys, how incredibly grounded they remain in the midst of this insanity. For example, Harry left home at 16, and has been doing this for 3 years, he's the youngest, and for that to be your life and to be so normal is incredible, and for me that's the most impressive thing. These guys come from great families, and those are their roots."

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  • One Direction: This Is Us World Premiere - London

    Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik and Liam Payne of One Direction arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Simon Cowell arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    (L-R) Louis Tomlinson, Zayn Malik, Niall Horan, Harry Styles and Liam Payne arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Louis Tomlinson arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Harry Styles arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Harry Styles of One Direction arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik and Liam Payne of One Direction arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Zayn Malik arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Zayn Malik arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Fans gather ahead of the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Fans gather ahead of the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Fans arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik and Liam Payne of One Direction arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik and Liam Payne of One Direction arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Harry Styles arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    (L-R) Louis Tomlinson, Zayn Malik, Niall Horan, Harry Styles and Liam Payne arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Harry Styles arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    (L-R) Louis Tomlinson, Zayn Malik, Niall Horan, Harry Styles and Liam Payne arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    (L-R) Louis Tomlinson, Zayn Malik, Niall Horan, Harry Styles and Liam Payne arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    A general view of One Direction arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    (L-R) Louis Tomlinson, Zayn Malik, Niall Horan, Harry Styles and Liam Payne arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Zayn Malik arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Zayn Malik arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Morgan Spurlock arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Morgan Spurlock arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    A crying fan arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    A fan in a wedding dress arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Morgan Spurlock arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    David Seaman and Frankie Poultney arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    David Seaman and Frankie Poultney arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Tony Adams arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    David Seaman (L) Frankie Poultney (2nd l) and family arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Simon Cowell arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Simon Cowell arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    David Seaman and Frankie Poultney arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    A fan in a wedding dress arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Simon Cowell arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    David Seaman and Frankie Poultney arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Morgan Spurlock arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • One Direction: This Is Us World Premiere - London

    Morgan Spurlock arriving for the World Premiere of One Direction: This Is Us, at the Empire Leicester Square, London.

  • Harry Styles

    Harry Styles arrives at the UK Premiere of 'One Direction: This Is Us 3D' - VIP Arrivals, on Tuesday August 20, 2013, in London. (Photo by Jon Furniss/Invision/AP Images)

  • Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik, Liam Payne

    Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik and Liam Payne arrive at the UK Premiere of 'One Direction: This Is Us 3D' - VIP Arrivals, on Tuesday August 20, 2013, in London. (Photo by Jon Furniss/Invision/AP Images)

  • Harry Styles

    Harry Styles arrives at the UK Premiere of 'One Direction: This Is Us 3D' - VIP Arrivals, on Tuesday August 20, 2013, in London. (Photo by Jon Furniss/Invision/AP Images)

  • Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik, Liam Payne

    Harry Styles, Niall Horan, Louis Tomlinson, Zayn Malik and Liam Payne arrive at the UK Premiere of 'One Direction: This Is Us 3D' - VIP Arrivals, on Tuesday August 20, 2013, in London. (Photo by Jon Furniss/Invision/AP Images)

What's he learned from his time with the band, the best part of a year of his life, taking in a tour, Madison Square Garden, and days with their families? "Work hard, stay humble and if you can do that, then you can accomplish a lot."

Spurlock, who doesn't call himself a massive fan of the band's music - "it's all relative" - nonetheless reveals that he has been so immersed in the creation of the film that, a year on, he dreams of the band every night.

"I still hear it in my head," he admits.

"I have been dreaming about One Direction now for going on 12 months, me and all the fans, I have so much in common with 17 and 18-year-old girls.

"Last night I went to bed and there I am dreaming about One Direction yet again. At some point something else will turn up in my dreams instead. I'm not sure when it will happen, but hopefully some time soon."

'One Direction: This Is Us' is in UK cinemas from 29 August. Watch the trailer below...