The legendary rocker, 79, was once moved to draw penises on the passport photo pages of Danny Jones and his bandmates Tom Fletcher, Dougie Poynter and Harry Judd, leaving them stunned and red-faced at customs.
Jones, 37, recounted the tale on the BBC One comedy show Would I Lie To You? earlier this month.
Admitting the story was true, Jones revealed that the “Da Ya Think I’m Sexy?” singer had appeared on the same bill as them at a gig in Ireland, and offered them a flight back to the UK.
He explained: “Rod said, ‘Do you want a lift? I’ll give you a lift on my jet.’ Then he said, ‘I need your passports.’
“So we get on the plane, give our passports to him and then fly to London.”
Although Stewart’s scribbles on the band members’ passport pages went unchallenged by border control entering the UK, American immigration officers were not so understanding when they later tried to enter the US.
Jones continued: “We get a call from our tour manager – I think he was applying for a visa.
“Then he was like, ‘Guys, bad news.’ Rod Stewart had drawn willies on our heads. It wasn’t fun travelling around – every customs [agent] was like, ‘You think that’s funny?’”
The “All About You” vocalist also noted that although they previously tried to explain their vandalised passports as Stewart’s doing, they eventually gave up as staff often didn’t believe them. He added: “We stopped saying that.”
The bandmates eventually applied for new passports to avoid further embarrassment.
Last year, Judd, the band’s drummer, opened up about why McFly decided against taking part in the Eurovision Song Contest back in the early 2010s.
“They were really trying to get us to do it, but it wasn’t right for us,” he told Metro.
Part of their hesitance came from seeing the competition as a “good place for new artists to be discovered”.
However, as an established, Brit Award-winning act by then, McFly arguably did not need the additional exposure. Still, Judd stated that the door is not completely closed on an appearance in future years.
“It’s a difficult one because it’s a great platform, you get seen by European countries – I guess never say never,” he added.
Would I Lie To You? is on BBC1 on Fridays at 8pm and available on BBC iPlayer.