Mumford & Sons' new album shows they have lost their "innocence".

The folk-rock group will release 'Babel' in September -- the follow-up to the huge album 'Sigh No More' -- and think the record is an improvement on their first offering.

Frontman Marcus Mumford said: "We've broadened our minds a little bit more. There's a slight loss of innocence, of the purity of the four instruments, but to us it sounds better. Also, our harmonies have got better."

Since the release of their first album, the group have spent a lot of time in the US but were determined to record 'Babel' in their native UK.

Keyboard player Ben Lovett added to NME magazine: "We're proud to be a British band. When we were talking about where to record the second album, the decision to record it in the U.K. was unanimous. It's part of our roots, it's our home soil, it's where we came from."

The band have previewed new material at live shows since 2010 and say it was handy to see what would and wouldn't work on the record.

Bass player Ted Dwane said: "We tried some stuff live -- some of it's been really successful, some of it hasn't. But the weak songs make themselves apparent really quickly."