So according to this article it was a case of jumping into the Core database and setting read and write permissions on the Move To item.
However I am still seeing:
For my custom role I have ticked Read and write for both item and descendents.
I have also ticked Read and Write in the child Move To item.
I don't believe that deny setting would affect my custom role as it's not a limited content editor.
Not quite sure why I'm still seeing this permission denied error.
I have confirmed using the access viewer that I think I should have permission to it:
The item I'm trying to move is under workflow - but I have locked it for editing so I should have write permission on that item in order to move it.
I have also tried clicking Create and Delete in the Copying and Move to security rights.
I have also tried updating
/sitecore/content/Applications/WebEdit/Ribbons/WebEdit/Page Editor/Edit/Move Page
to grant this role allow on read, write, create and delete.
But am still getting an error when trying to move something.