The two rappers announced in 2013 that they had inked a deal for their joint memoir of the group's history following the death of third member Adam 'MCA' Yauch the previous year (12).

They had eyed a 2015 release date but Horovitz has now revealed the tome will not be out this year as it is taking the pair too long to complete.

He tells Q magazine, "We've got pages!... How it's going to fit together, I don't know, but we've got some ideas. It's interesting. It's fun."

Yauch died aged 47 after a battle with salivary gland cancer.