Tesco has seen some supply disruption to the island of Ireland since a post-Brexit trade deal with the European Union kicked in on 1 January, said Ken Murphy, Tesco, CEO.
Tesco, on Thursday followed rivals in reporting buoyant Christmas trading, as pandemic restrictions meant people splashed out on celebrations at home.
The group said UK like-for-like sales growth was 6.7% in its third quarter to 28 November, accelerating to 8.1% in the six weeks to 9 January.
"We delivered a record Christmas across all of our formats and channels," said Murphy.
Tesco's update follows strong Christmas trading reports from No. 2 Sainsbury's, No. 4 Morrisons and No. 7 Lidl GB.
Industry data published last week showed the supermarket sector benefited from unprecedented Christmas demand, with shoppers spending £11.7 billion ($16 billion) on groceries in December.
Working From Home
Restrictions to contain the virus mean many people are working from home and the hospitality sector is closed.
Adding to the demand for food and drink, many of the five million or so Britons who normally travel abroad for Christmas had to stay at home.
Tesco estimated additional COVID-19 costs would be £810 million in its 2020-21 year, up from £725 million forecasts in October.
But it still maintained its guidance for 2020-21 retail operating profit before exceptional items of "at least" the same level as 2019-20's, excluding the repayment of £535 million ($729.3 million) of business rates relief.
Tesco also continues to expect to report a loss for Tesco Bank of between £175 million and £200 million for the year.
Shares in the group, down 3% over the last year, closed Wednesday at 242.1 pence, valuing the business at £23.8 billion.