Oyster Bay (Merlot/Chardonnay/Sauvignon Blanc normally £8.99, currently down to £6.49, and get extra 25% off if you buy 6 bottles makes it £4.87 (if my calculations are correct).
Not as cheap as asda Sauvignon Blanc posted earlier for £4.48, but still a good deal if Tesco is closer to you. Also available on 3 types of Oyster Bay! Merlot/Chardonnay/Sauvignon Blanc.
Other wines available with extra 25% off ontop of any existing discounts from Tesco.com (don't think it applies to tesco wine by the case). Also mentioned earlier thread by" nicster08"