Not really my area, but what I have been able to research:
I believe it is a Harington type 1 a, b or c. I can't see from the pictures, but on "a" the mintmark is on the cushion of the crown, on "b" it replaces the jewel on the circlet of the crown and on "c" it is below the crown. As far as I can see, all type 1s have the symbol you highlighted before FRA, but this is not a mintmark. I can find no name for it, but it looks like a Saltire over a Mascle. On type 2 Haringtons the mintmark is on the reverse in the same place before the FRA as the symbol, but I am fairly sure yours is type 1 as it is too small for a type 2.
Thanks for the help all, and for the welcome back message! Time in between coin finds has been long, but hopefully we'll find more as we scour the foreshore.
Reading up it seems like the only difference between Harrington 1a and 1b would be the privy mark, which I think will be too hard to locate due to condition. And I've found reference to the star (mullet?) between the letters, but there was no mention of its significance.