Tesco's like-for-like sales fell by 2.4% over the Christmas period, the company announced, blaming a "weaker grocery market".
Rival supermarket Sainsbury's revealed its "best Christmas ever" on Wednesday but warned on consumer spending going forward.
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A suspected gunman held people hostage inside the store, police said.
Popular channels including Dave and Gold disappeared from sets after a business dispute went unresolved.
Police said it was not clear whether anyone was still inside the store.