Hi Tony,
Thank you very much for that. I managed to drain the system enough to undo and inspect the union. After some PTFE tape, it has made it a little better but still not fixed it.
My next line of attack will be replacing the plastic pipe and joint.
Unfortunately, I can't seem to upload any photos as I am on a Mac, therefore, do not have a 'My Media file', the forum seems to be set up for PCs.
I do, however have an Android phone which I could try it on, so I'll try with that.
Once again, thanks for your time and help and I'll let you know how I go.
All the best - Daniel