Phylum: Rhodophyta   Family: Rhodomelaceae

Polysiphonia elongata (Hudson) Sprengel, 1827

Elongate Siphon Weed

Dickinson (1963) gives a more evocative common name: Lobster Horns. It occupies a wide range of coastal positions from sheltered bays to exposed sublittoral, attached to hard substrates

References: 
Dickinson (1963) - British Seaweeds;
Maggs & Hommersand (1993) - Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 3A Ceramiales