Confidence: It might be this.
Notes: Rock Sea-spurrey should be densely stickily-hairy according to the books, so I don’t think it’s that species. Without seeing the seeds things now start to get tricky. It has too few stamens to be Greater Sea-spurrey, so that narrows it down to Sand Spurrey or Lesser Sea-spurrey. Given the habitat, which looks like the edge of a salt marsh, I’m going for the latter (which was your second choice). But I could be wrong