Just wanted to say many thanks to all the contributors on this thread. I was almost out of the front door on my way back to the shop when I thought 'let me check on the news groups'. Glad I did. I now don't have to change all my passwords to email accounts, ebay etc etc. Although Tesco was willing to refund or replace, I wasn't willing to hand over my life.
Thanks everyone, the 30 second power button push worked a treat.