First off, I am sorry for posting another topic on the same subject - and hence for wasting bandwidth etc.
I wanted to post in my old topic but saw that it was archived and hence unavailable for me to do so.
I just wanted to update those of you that very kindly helped and advised me regarding my lens and the possible problem(s) I was having.
I received it back today and am pleased to say that it is a lot better in regards to quality and sharpness. It seems like it was £154 well spent.
Perhaps the most singular evidence I have of the 'improvement' arises from the uv filter versus no uv filter aspect.
Before I sent the lens off for repair, I could see no difference, at all, in terms of image quality or sharpness when using a uv filter or not.
Now, the difference is clear. The quality and sharpness are greatly improved when not using a uv filter. (Even at the 100mm end).
Unfortunately I have not taken it spotting yet but am pleased with my initial findings.
I just wanted to let you all know of my outcome, in case any one else finds themselves in a similar predicament.