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, D.M., Whitton, B.A. & Brook, A.J. (2011) - The Freshwater Algal Flora of the British Isles;
The Marine Life Information Network