Head buyer Jonathan Butt said: "Although three-for-two has really increased our volume in Champagne and sparkling, we thought we might be missing out on customers who want to come in and just buy one bottle - the distress purchases."
Customers buying three bottles of Champagne and sparkling will still get 20 per cent off the total price.
Also, at the Thresher Group's tasting this week, buyers said Spain and France were enjoying better growth than New World wines.
Butt said: "People are bored with the offering of the New World - disappointed with the quality that they're getting via places like Australia. The way it fills the market with cheap, bad or poor-quality wine will come back to haunt them. The Old World has not prostituted itself to the whims of BOGOFS and chasing market share."
Thresher's next in-store varietal promotions will focus on Sauvignon Blanc, rosé and organics to coincide with the Soil Association's Organic Fortnight in September. It is also set to increase its Origins own-label with a number of additions from France, South Africa, Chile and Italy.