Trevor
If you are not familiar with Ashton centre then, I agree, it is easy to miss the notices.
If you do park in Ashton again then the two free car parks are situated:
* parallel with Hilton Street (access it via Ladysmith Avenue) but don't go through the yellow barrier because then you are on Aldi and they fine you if you overstay.
* Market Square (access this via Garswood Street).
If you park on these then it is free and there is no time limit on your stay