Retail chain John Lewis Partnership saw an 11% rise in sales in the last week of 2018 compared with a year earlier.
The partnership includes both John Lewis department stores and Waitrose supermarkets.
John Lewis reported very strong sales on Christmas Eve itself - which was included in the last week of trading - as customers bought last-minute gifts.
Waitrose sales provided most of the year-end boost, rising 19.2% on the same week a year ago.
Gift food sales at John Lewis doubled, while beauty and well-being products saw a 25% increase.
However, in the previous week, ending on 22 December, sales across the partnership fell 4.8%. Its financial year so far has seen sales remain flat in both Waitrose and John Lewis.
A Waitrose spokesperson said: "As always at this time of year, our sales figures are heavily distorted by the fall of Christmas and New Year. Both these weekly performances were in line with expectations."
The strong figures at Waitrose are likely to have been distorted by Christmas falling on a different week to last year, therefore boosting 2018 sales.
Nicholas Carroll, senior retail analyst at research group Mintel, said: "There has obviously been a big distortion by the way the last week has included Christmas Eve, and we will get a better picture in few days time when we get sales for the whole of the six week Christmas trading period.
"Even so at a time when retailing is meant to be on its knees, the John Lewis figures that we can see look fairly good and they imply an increase in sales of about 4% over the two week period."
The final week also saw the start of some clearance sales. John Lewis said that electrical and home technology sales rose 3.1%, with Apple products performing particularly well and communication technology products also up.
Unsurprisingly, in the middle of the holiday week, sales of Waitrose's fresh and frozen food did well, rising 22% on the same period last year.