Thank you so much for getting back to me so quickly, I really appreciate it.
It's good to hear that you are working on the issue - however long it takes.
Using your instructions, I have been able to remove the plugin using the following steps:
For anyone else in my position, here's how I removed the plugin:
1. Install My Adminer plugin (this allows access to the database from within Moodle)
2. SSH into moodle and remove the 'btec' folder from /moodle/grade/grading/forms
3. Remove the entry from mdl_config_plugins where plugin='gradingform_btec'
4. Finally remove three tables that where created when the btec plugin is installed. They all begin with "mdl_btec". This needs to be done to allow the plugin to be reinstalled.
Thanks again for your reply, it helped get me on track.
I do just want to say that this is an excellent plugin and I will be reinstalling it on the live server once it has been fully tested on the development server.