Phylum: Ochrophyta   Family: Alariaceae

Alaria esculenta (Linnaeus) Greville, 1830

Dabberlocks

A tough plant, growing on rocks with a root-like holdfast. Found along the Atlantic coast in wave-exposed situations, in the shallow subtidal. A long narrow seaweed not easily confused with others

References: 
Fish & Fish (2011) - A Student's Guide to the Seashore;
Bunker, et al - Seaweeds of Britain and Ireland