One Direction fans are always trying to "outdo each other" on Twitter, claims a top psychologist.

Last week GQ magazine unveiled the group's individual covers, with the tagline under heartthrob Harry Styles' reading: "He's up all night to get lucky."

The tongue-in-cheek expression incited an outbreak of irate tweets from One Direction fans, with one writing: "I'M F**KING PI**ED AT HOW THEY PORTRAYED YOU, YOU ARE NOT A GOD DAMN MAN W***E, YOU ARE A CUPCAKE.

Another follower wrote: "I'M GONNA BOMB YOUR HEADQUARTERS! DIRECTIONERS ARE THE WORST FANDOM TO MESS WITH! F**K YOU GUYS! (sic)."

Psychologist Dr Jane McCarthy says One Direction fans are taking their devotion too far.

Explaining to British magazine Heat she said: "The fans on Twitter are seeing if they can outdo each other. They're in competition to see who can be the most defensive of their heroes by writing the most explicit tweet."

One Direction star Zayn Malik has previously discussed the problems the band face as a result of security fears surrounding their devoted fanbase.

He said: "We don't get to see [the fans] as much as we'd like to anymore because of security issues and stuff."