Hi rhmb, Thank you for your inputs, really appreciate the help.
Since posting I have got a slightly better understanding of what Affinity Photo is doing and sorry for using the wrong terminology but I was actually trying Edit using the Affinity Develop Extension and Edit in Affinity Photo Extensions rather than "Edit with" as I had already sussed out that the latter was not without it's problems.
As for the file size I think I now understand what is going on; when used as an extension to Apple Photos, only one large file gets created in a folder in the library folder and this gets overwritten each time a new image is edited so doing it this way means that the original image before it was edited in AP cannot be recovered.
I have also tried editing the image directly in Affinity Photo and then exporting to Apple Photos which does mean I can revert back to the original because an image with the .afphoto gets saved but this is not very efficient in terms of disk space.
I have had my Olympus cameras since August so I have tried Workspace over the past few months but I don't like it hence why I bought Affinity Photo which I do like and for £23.99 worth the price even if I'm not going to use it as my main edit application.
I was using Apple Aperture until it became unsupported and switched over to Apple Photos which has been fine for what I want; it's just really annoying that Apple have still not provided ORF support for the OM-D E-M1 Mark III but having said that the processed JPG that the camera saves is actually quite good so I think I will persevere with JPGs and use Affinity Photo as and when I feel I need to do something a bit more complex with layers which is something Apple Photos cannot do. Up until buying the Olympus, I was exclusively shooting Nikon NEF RAW images so never had any issues with Apple Photos, my latest Nikon is a Z7 which I use as well as the Olympus and with over 11k images stored I find Apple Photos organisation features really useful here why it will remain as my main photo application.