Update 8:
I used some of the information from the official OS map to alter the terrain around the southern coast a bit.
We now have more forest and swamp terrain there and hunters edge has its landmass now.
Additionally I altered the sea, so we have this unknown island and a bit of an archipelago.

Here is the link to the sketch:
https://www.dropbox.com/s/r2z5byq2k5x773q/Sketch8.png?dl=0

PS: Can I somehow edit the thread title? I think the current does not fit well anymore.