Online sales rose 12.8% last month, helped by the lack of Easter holidays, which tend to drive consumers out of the house and to the shops.
Meanwhile, for the three-month period to March, food sales were down 2.7% on the year before.
It accelerated a decline since last autumn which is seen as likely to be exacerbated by a coming price war as the major supermarkets aim to head off the threat from discounters Aldi and Lidl.
For non-food, the most recent three-month period saw like-for-like sales up 3%.