Phylum: Ochrophyta   Family: Scytosiphonaceae

Scytosiphon lomentaria  (Lyngbye) Link, 1833

Beanweed

A cylindrical and hollow seaweed, variably brown, unbranched, and irregular constrictions being a feature. Best looked for in upper-shore tidal pools, attached to rocks and limpets

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