The British boy band are currently on tour in America and the success and screaming girls which have followed them has left their mentor suffering sleepless nights.

The group's Louis Tomlinson said: "He's really, really excited about the reaction we've had out here and has said he's not sleeping ­properly because he keeps thinking about us and how it's going. He's far too excited to sleep. Which is quite cool."

The group - who's debut album 'Up All Night' is tipped to top the US charts tomorrow (18.03.12) - were initially told it would take them much longer to crack the difficult US market, but micro blogging site twitter has helped them gain fans.

Singer Liam Payne told the Daily Mirror newspaper: "Our tour manager told us it would take three years of hard graft to do well in America. So for it to have taken off as it has is incredible.

"Twitter has been a major factor in getting our name out there in the States. Just as twitter followers have gone up, so we have, too."

15,000 girls turned up to see the 'What Makes you Beautiful' band - which also includes Niall Horan, Zayn Malik and Harry Styles - perform on 'The Today Show' in New York, but they shy away from comparisons to the Beatlemania which swept the US in the 60s.

Louis added: "To be compared to something that was so big in its day is amazing.

"To be our generation's Beatles... Wow. It is hugely flattering, but I'm not sure how seriously we can take it because it seems so unrealistic."