Studio pottery mugs with anchor mark not Anchor Pottery, John Buchanan.

Hi there, I have six of these mugs all with impressed anchor marks below the handle. At first I thought they were made by Anchor Pottery/John Buchanan, but the mark isn't exactly alike in addition to being absent of a signature. Any ideas of the maker?

In the Yates-Fourner studio marks book there are a number of potters besides John Buchanan, who used an anchor mark. Including William Marriner, Tony Moody,Peter Smith and even Grayson Perry! However none of those marks fit this any nearer than John Buchanan's Anchor pottery
Buchanan's Anchor Pottery was around for a long time, and none of these marks are necessarily set in stone. There can easily be variations that people are not generally aware of.
Naomi might know more, as she has a much wider knowledge of International marks.