Tesco frequently has attendants monitoring the self service checkouts; if someone sees that your items are going through for £0.01 (the prices are displayed on the monitoring screen that the attendant can see) you're probably going to have a bad time (banned from the store at the very least).
Once again, depends where you go. I've been in supermarkets where the self checkout registers mess up so frequently that the attendants basically rush over, swipe their card, whack something on the keypad, then disappear to the next red flashing light. They rarely check anything!
Don't discount it to £0.01, that is just stupid. The obvious scam here is to take high value items and mark them down dramatically. For example, marking a £200 phone down to £20.
Not worth it...