Saw an official Tesco Ad in yesterdays Mirror.
Cant post a link but basically it said.
"We're giving all our pay as you go customers £5 free credit to say thank you for voting us no.1 for customer satisfaction.
To redeem your credit text THANKS to 26929
Credit will be added to your account within 48hours.
Customers must have topped up ON OR BEFORE August 12th to qualify.Offer ends Sunday 15th August at midnight. "
Their latest press release confirms they won the award.
See:
http://www.tesco.com/mobilenetwork/content.aspx?page=12