It's amazing what a small amount of collimating can do.
I adjusted the Scope after suspecting that the mirror was out of line. I used a bright star and de-focused, I could see that the concentric rings were skew whiff.
I tried to adjust one of the screws on the scope, it was too tight, so I tried another, which was looser. I turned it a small fraction and looked back in the eyepiece. It was better, I turned it a tiny bit more, and it now seemed OK. I went back to look at Mars and WOW!
I could see loads more detail. I could now use the barlow lenses without the fuzzy blobs as before. I'll need to spend a bit more time doing a proper job on the collimating, but for the time being it's made a difference of 100%
The image above was taken a few minutes before the one below.