Updated Tesco's nationwide till system failed this morning, leaving the country's biggest retailer able to sell only via self-service checkouts.
Managers closed some stores in response to the glitch.
A spokesman for the firm confirmed it was suffering IT problems, and was investigating.
According to reader reports, the problems began as soon as stores opened this morning. It's common practice for large corporations to roll out major software changes overnight on Sunday.
We'll update this story as more information comes in. ®
According to PA, about 100 stores are affected, and the problems are being rectified by rebooting the checkouts.