Domino's Pizza Group (DOM) , the U.K. unit of the American food giant Domino's Pizza Inc. (DPZ) - Get Domino's Pizza, Inc. Report , saw shares fall Wednesday despite revealing better-than-expected third-quarter sales and aggressive expansion plans.

Shares in Britain's biggest pizza delivery firm slipped by around 2.5%, outpacing decline for the broader FTSE 250 benchmark, following a trading update for both its U.K. and European operations.

The stock has, however, risen more 18% since the company completed a 3-for-1 split on June 27.

TheStreet Recommends

The company reported like-for-like sales grew 3.9% in its fiscal third quarter, which ended on Sept. 25, thanks to a surge in online orders. Digital channel sales rose by more than 18%, the company said, adding that more than 80% of its delivered sales were generated through online platforms such as Domino's mobile app. Group system sales, it said, were up 11.5% to £237 million ($291 million). Domino's also said it would accelerate new store openings in the U.K. to 80 this year, up from a previous target of 70. 

Underlying sales in Switzerland rose 16.7% in the quarter, the company said, and 7.6% in Ireland.