The band, whose debut single 'All Time Low' shot to number one on iTunes after being released last night, admitted their excitement about the news on Twitter.
In a series of posts, they wrote: "['All Time Low'] number 1 on iTunes right now!
"AHHH #1 I TOLD YOU WE COULD DO IT! haha (sic).
"How was everyone's weekend? Ours was superb - great gigs and iTunes no.1! Now very excited for this week's shopping centre tour."
Band member Siva Kaneswaran added: "My god that's sooo good!!! Thank you to all the friends and family. It means so much to us!ssooooo much!"
The group are signing copies of the single at HMV stores across the UK this week.