Ok Harry
To confirm my theory that your machine's colour management is over saturating an image that does not have an embedded ICC profile I have constructed a simple web page that contains the same image with and without an ICC profile embedded. Saved in Photoshop with and without the ICC Profile box ticked.
http://robertstocker.co.uk/Harry/test.html
another area to investigate is the "Advanced Tab" on The color management window(you were looking at the device tab earlier).
Do you have say wide gamut or Prophoto selected.