Hi there,
I’ve been tinkering and have managed to solve the issue! So I’m sharing how I did it here in case others have the same problem:
1. Downloaded my wp-config.php file from the FTP
2. Resaved this as UTF-8 format (not UTF-8 BOM / not UTF-8 no BOM)
3. Uploaded file to FTP
Done… I’m not quite sure how this issue arose in the first place as I hadn’t been fiddling with anything but I’m just happy to have access now!
Thanks to @t-p for the assistance.
Best wishes
Kam