Royal Mail has published a list of 28 areas suffering from limited delivery services as more of its workforce is affected by Covid-19.

The zones – comprising 27 in England and one in Northern Ireland – are no longer receiving regular post because of the high numbers of Royal Mail staff who are either off sick or self-isolating.

The affected areas include 13 in or near London, while others include Leeds in West Yorkshire, Chelmsford in Essex, Widnes in Cheshire and Margate in Kent.

With some affected residents complaining of not having had mail delivered for more than a month, fears have also arisen that elderly residents will not receive notifications of when a coronavirus vaccine is available to them.

Despite our best efforts and significant investment in extra resource, some customers may experience slightly longer delivery timescales than our usual service standards

Valerie Wallbank from Hainault in north-east London told the Ilford Recorder she had not received any mail since December 12.

“It’s quite serious,” she told the paper. “Some people are not bothered because they do everything online but for some of us it’s quite important.”

The issue has prompted calls, including from MPs and the Communication Workers Union (CWU), for postal workers to be added to the priority list of people receiving coronavirus vaccinations.

In a statement published with the list on its website, Royal Mail said it was “working hard to deliver the most comprehensive and high quality service we can to all our customers” despite the pandemic and the associated rise in pressure on delivery resources due to increased online shopping.

“The combination of greatly increased uptake of online shopping, and the ongoing Covid-19 restrictions, mean that all delivery companies are experiencing exceptionally high volumes,” the statement said.

“Every single parcel and letter is important to us. Despite our best efforts and significant investment in extra resource, some customers may experience slightly longer delivery timescales than our usual service standards.

“This is due to the exceptionally high volumes we are seeing, exacerbated by the coronavirus-related measures we have put in place in local mail centres and delivery offices to keep our people and customers safe. In such cases, we always work hard to get back to providing our usual level of service as quickly as we can.”

Ilford MP Wes Streeting said while it was understandable that Royal Mail was being affected by the virus, the problems were having “a serious knock-on impact on people getting important NHS correspondence, both about their vaccination and also other routine appointments”.

“I have been told locally that Royal Mail are prioritising the delivery of parcels to get the backlog down, but I wonder if there is a way for NHS correspondence to be clearly labelled as such and prioritised for delivery,” Mr Streeting told The Daily Telegraph. “No one wants to see a situation where people are missing their vaccination appointments.”

On its website, Royal Mail advises people in the regions who have been left a “Something for you” card from the service to check its website to learn revised opening hours for when they can collect the item.

“If we’ve not left a ‘Something for you card’, and you do not have alternative arrangements in place, we’re sorry that your mail will not be available for collection,” the advice says.

The Daily Mail has reported the CWU has called for the Government to prioritise postal workers on the list of people in line to receive Covid vaccinations, and that BT has also called for its engineers to be added to help with its call-out capabilities.