I developed a B&W film from the camera last night and the results were spot on.
I've recieved some fresh C41 dev and blix of a different brand.
Tried re-blixing the colour existing dodgy film - It came out a little lighter but no great difference.

I suppose my next step is to try processing colour again using my new chemicals.
Poor chenistry seems to be the most likely option to me. If it's not then I'm stumped!

Oh, and Primefilm 3600u scanners are officially dreadful - I am now hunting for something better.