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Til now I didnt realise we had more than one species in our waters. The vast majority of sqauts I see are drab green/brown as you describe above, I thought those were females and the above one was a male. Maybe there is more to it as you say. I have a very well marked juvenile photographed, which I'll put up soon, be interesting to hear what you make of it...
Yes, you've moved on since this - we all have!
This was posted less than a day after Chris' ID above http://www.ispotnature.org/node/248458
It has an interesting picture and comment trail.
I have Chris to thank for informing me of quite a few seashore things I didnt know, by correcting various IDs I have put up.
Lat/Lng: 55.0812, -6.0517
OS grid ref: NW415838