Royal Mail has apologised to SE1 residents and businesses who say they have not received postal deliveries for up to a week.
Many local residents have this week reported long gaps between postal deliveries in SE1.
"We apologise to customers in Southwark who may not have recently received the service they expect and deserve from Royal Mail," said a spokeswoman for Royal Mail.
"We can reassure customers that mail is going out for delivery on all rounds in Southwark every day.
"We regularly review our delivery operations as the nature of the mail we handle changes – with more parcels and fewer letters in our network. This may mean that our postal walks change or customers receive their deliveries at a different time. There have been no compulsory redundancies as a result of this review and we remain committed to providing a first class service to our customers.
"Recently, major roadworks in the area and a temporary higher level of short-term sick absence in the office may mean that some deliveries may be slightly later than usual. We have put contingency measures in place, including drafting in extra resources, to improve services to customers in the run-up to Christmas."
The spokeswoman added: "Any customer who has concerns about their mail deliveries should contact the Royal Mail customer services team on 03457 740 740."