Phylum: Charophyta   Family: Characeae

Lamprothamnium papulosum  (K.Wallroth) J. Groves

Foxtail Stonewort

Found in fairly still, brackish, nutrient-poor water on sand, gravel, small pebbles and silty substrata - The Marine Life Information Network

References: 
John, Whitton & Brook (2011) - The Freshwater Algal Flora of the British Isles;
The Marine Life Information Network