Far from certain if my suggestion is correct so any comments will be great. Found on an old wooden post at high tide level.
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
This is a link to the OPAL lichen survey id page http://www.opalexplorenature.org/Lichenguide there is also a link to a lichen key that might help you.
Whatever this is, it is not one of the very few lichens, growing on trunks and twigs, covered by the OPAL survey. Everyone should know about the OPAL survey, and if they don't they should follow this link, but I am afraid that it will not help here.
This is not a Candelariella, and I doubt that it is a lichen at all.
It would need to be investigated with a microscope and I suspect that it is actually a seaweed - either one of the green algae that occur at the tops of shores - though not one I know - or just possibly one of the yellow-green algae (Vaucheria and allies) that might also occur in such a situation.
This is a very good photograph of something interesting. I wish I knew what!
Lat/Lng: 53.629, -0.077
OS grid ref: TA272164