Great topic. I also have experiences the store practices mentioned above, I remember the kettle and toaster I purchased many years ago in an SM department store which were ceremoniously removed from the boxes and I was shown that they worked,,,,,,,,, including waiting for the water to boil in the kettle in an aisle in the middle of the store, I asked why and as above was told "We showed you it works Sir and no warranty" OK, fine. We have purchased major items that came with a 12 month warranty, a TV we purchased played up after 6 months, contacted the store and within a day or 2 a technician arrived on our doorstep and spent an hour pulling it apart and repair,,,,,,,, no charge and an apology.
I did find these links which are an interesting read. The first is basic but outlines the law. The second is the act.