Heighleygate garden centre just outside Morpeth today had boxes of free samples on their shelves beside large sized for sale packets of the same brands.
Separated out around the pet food section there were free sachets of dry ferret food, kitten food and cat food, all on shelves in the manufacturers boxes marked 'free sample'
I left with 12 packets (3 flavours x 4 packets), and a few others were helping themselves but not many it looked like this was a regular thing (though i've never noticed it before and it wasn't advertised).
I didn't buy anything, just picked these up and left with them in my hands openly - a member of staff smiled and nodded at me on the way out so there doesn't seem to be a limit, a need to buy anything or a need to put the free samples through the tills.
I have no idea if this is available in other stores.
If you can't get into the store http://www.wellbeloved.com/products/trial_sample.aspx
says it gives away free samples every day - but they always seem to have gone for that day when i try