Found on the bottom shelf, end of row with other discounted 'winter' products. Both sizes of bag were 2p!
This was in the St.Pauls Road, Bournemouth branch.
They also had screen wash and deicing fluid in hand spray or aerosol.
Hopefully we won't need it again this year but good to put in the garage ready for next year.
I've tried to post the photo of my receipt but it's not uploading.