On Monday the supermarket unveiled a "Brand price match" commitment against Tesco on big brands such as Walkers, Persil, Andrex and Coca-Cola.
Thomas said: "We are not undercutting Tesco on price but we are reassuring customers that we are the same price.
"We are clearly doing this because we want more customers shopping with us."
The commitment will cost Waitrose an estimated £26m, but analysts believe the investment will pay off.
Alan Treadgold, head of retail strategy at ad agency Leo Burnett, said: "Waitrose is saying that it stands for food quality, but is no longer disadvantaged by price.
"It is not a vast amount of money to spend – grocery retailing is about growing the basket size."
The promise follows the success of a similar commitment by Ocado, which has helped the online grocer grow its sales.
.jpg)
.jpg)