He replaced Martin Lamble, who had died on 12 May 1969 in a road accident on the M1 motorway, as the drummer for Fairport Convention.

[1] Meanwhile, he had also contributed to numerous studio recordings such as the Morris On project, Nick Drake's Bryter Layter, Steve Ashley's "Stroll On" sessions, Steeleye Span's debut album Hark!

The Village Wait, John Martyn's Solid Air[2] and Harvey Andrews' album Writer of Songs.

Mattacks also played on Nine (1974) but left halfway through the making of the follow-up Rising for the Moon, following an altercation with engineer Glyn Johns.

[3] Some of Mattacks' most notable participation in studio recordings in the late 1970s are the work on art rock studio albums by Brian Eno (Before and After Science) and 801's Listen Now, as well as several Ashley Hutchings-related folk rock projects (The Compleat Dancing Master, Son of Morris On etc.).