Anmar Frangoul for CNBC:  A common sight in the British countryside, bracken -- a type of fern -- is now being hailed as the next big source of biofuel. 

Based in the south west of England, Brackenburn produces "brackettes" – biomass pellets made from bracken that they shred and compress into briquettes which produce much more heat when burnt than oak.

"In our estimation there's 2.5 million acres of bracken in the UK… it's a huge area," Barry Smith, Brackenburn's marketing and sales director, told CNBC in a phone interview.

"Left unchecked, bracken encroaches by three percent a year… at the end of the day there's no use for it whatsoever," Smith added. "It's a nuisance and to call it a crop is kind of giving it a status it doesn't deserve."  Cont'd...