BBC.An Ocado spokesman said: "Staff absences across the supply chain may lead to an increase in product substitutions for a small number of customers as some suppliers consolidate their offering to maintain output."Supermarket websites struggled to cope last week as people surged to buy groceries when England went into a third lockdown.Social media flooded with images of empty shelves - similar to those seen in the first lockdown last year.Retailers have all said there is plenty of food in the supply chain and have urged people to shop normally.Ocado says there is plenty of food - but some lines will be limited.Ocado has told its customers that from Friday "changes to the UK supply chain have affected some of our suppliers and may result in.