Shoppers told not to buy more than normal
Supermarkets are seeking to reassure shoppers that there is no need to bulk-buy products as new lockdown restrictions come into force.
Asda asked its customers to "continue to shop considerately and not buy more than they normally would."
There was a surge in online grocery shopping after new lockdown restrictions were announced on Monday, but demand has since dropped back.
Stores said they have good availability and have increased delivery slots.
Tesco and Sainsbury's have doubled the number of delivery slots since March.
When fresh lockdown restrictions were announced on Monday there was a rush online by supermarket shoppers to book delivery slots.
That surge has since calmed down, but big supermarkets were keen on Wednesday to reassure customers that there is no need to bulk-buy, as stores would like to avoid a repeat of the panic-buying that was triggered by the first lockdown.
Asda said it "currently has strong product availability across its stores and depots and its colleagues are working around the clock to keep the shelves stocked."
Sainsbury's said it had "good availability and encourage customers to shop as normal. We aren't currently restricting products."
Tesco has had buying limits on various products since the first lockdown, and most recently limited items including eggs, rice, soap and toilet roll after freight delays in December as ports got snarled up.
Tesco said on Wednesday that it had "good availability in stores and online, with plenty of stock to go round, and we would encourage our customers to shop as normal."
Online surge
During the first lockdown supermarkets saw a huge spike in demand for online shopping as people tried to avoid mixing in shops.
The big chains have all increased their capacity to deliver food.
Tesco, the biggest UK supermarket chain, has more than doubled the number of online delivery slots available since the start of the crisis, and now has 1.5 million slots per week.
Not all of these get used across the UK at present, so Tesco has no plans at the moment for further slots.
Sainsbury's, the second biggest, has also more than doubled the number of its online delivery slots since March, and can meet more than 800,000 orders per week.
Asda, the third biggest chain, has upped the number of available weekly slots by 90% since March to 850,000, and by the start of April it's planning to offer 900,000 slots per week.
Morrison's, the fourth largest UK supermarket chain, said it had increased its online operation fivefold since March.
Coronavirus measures
Asda said on Wednesday that it was also doubling the size of its partnership with Uber Eats. From February Asda will offer a 30-minute delivery service from 200 stores.
Asda is also stepping-up Covid safety measures, including doubling safety marshal hours, more sanitation stations, increasing cleaning, and "adding a protective antimicrobial coating to customer 'touch points' in stores such as fridge and freezer handles, checkout areas, plus all trolley and basket handles".
The chain also has a virtual queueing app called "Quidini" whereby customers can sit in their car to wait for a slot in a store if it is busy.