Phylum: Ochrophyta   Family: Fucaceae

Fucus vesiculosus Linnaeus, 1753

Bladder Wrack

Found on the middle shore, even on exposed western coasts but more prolific in sheltered situations. Air-bladders often appear in pairs and the fronds have a pronounced midrib. Some examples are almost lacking in air-bladders which can cause consusion with other species

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