mrmgarside

An earlier suggestion by davethehacker works fine and is very simple.

Download a fresh copy of the plugin from this link (which evidently contains some files not included in the wordpress version):
https://github.com/tlovett1/custom-contact-forms/archive/master.zip

Then delete your current copy of the plugin from within your wordpress installation, and add the new copy as if it were a new plugin.

I was worried that i would lose my existing forms and submissions history, but all of this was retained, and all editing capabilities were restored.

sorry, probably a stupid question – not sure how to install this as wordpress installer won’t do it (since the folder already exists). Can it be done from within wordpress or do I need to ftp these files into the plugin directory? And will that preserve my existing forms and submissions?

Yes, what he said.
Version 7.8.4 of the plugin and wordpress 4.7 leaves no editing capability and no way to view messages within wordpress.
Any fix much appreciated