Thousands of households across Britain will not receive their post until after 5pm under a major shake-up proposed by Royal Mail.
The postal service wants to push back deliveries until later in the day as part of plans to deliver parcels more quickly.
With many online shopping orders now made late at night, bosses want postmen and women to set off on their rounds later to give time for “next day” packages to arrive at sorting offices.
But modelling of the changes has found this could mean more than 100 areas of Britain get their post at 5pm or later, the Telegraph can reveal.
Of these, 17 areas may not get their post until 6pm at the earliest, including parts of London, Cornwall, Cumbria, Wales and Scotland.
These include Abbey Wood, New Cross, Rotherhithe and Southwark in London, as well as Truro in Cornwall, Barrow-in-Furness in Cumbria and Arbroath. Those in Kinross, near Perth, may not be handed parcels until 7.30pm.
A Royal Mail spokesman on Friday said the figures were based on “high level” assumptions and no final decisions had been taken.
She added that all letters would be delivered by 5pm at the latest, compared to 4pm now.
They are also subject to negotiations with the Communication Workers’ Union (CWU), which represents more than 100,000 postal workers and is threatening nationwide strikes in the coming weeks.
An overwhelming majority of CWU members voted for industrial action a fortnight ago following a row with the company over pay and conditions.
The union claimed the changes to delivery schedules were “outrageous”.
A spokesman said: “The changes would see our members delivering up to five hours in the height of summer heat and in the darkness of winter.
“This is just one example of how Royal Mail are running down the postal service in the UK and why our members are balloting for strike action to defend it.
“Postal workers need and deserve the support of the public to win this battle.”
Royal Mail has given postal workers a 2pc pay increase backdated to 1 April already and is offering the CWU a 3.5pc rise which depends on improvements in productivity and changes to postal worker rosters.
However, the union has dismissed the offer of pay as a “serious real-terms wage cut” when compared to soaring levels of inflation, which is expected to peak at more than 13pc in October.
The union has 115,000 members in the company, which employs a total of about 140,000 staff. If the CWU cannot reach a deal with Royal Mail, it is threatening strikes that would be likely to take place this month.
It would be the biggest strike in what has already been dubbed the “summer of discontent”, after rail workers, barristers and airport staff all voted for industrial action, while teachers are set to be balloted in September.
Royal Mail has repeatedly locked horns with the CWU over modernisation plans.
It claims that in order to boost productivity and deliver more parcels, as letter numbers decline, it needs to introduce more automatic sorting machines and adopt seven-day working weeks.
Bosses argue this is in line with standards that customers have come to expect from rival delivery companies and that too much post is currently sorted by hand.
Royal Mail said moving to later delivery times would also allow more post to be transported by train rather than lorries, cutting the company’s carbon emissions.
A spokesman added: “We are in discussion with the Communication Workers Union about moving start times later to meet the growing customer demand for more next day parcel deliveries, and to reduce our environmental impact by moving more mail by rail over time.
“We have made it clear that these proposals are all subject to negotiation and detailed design, and no plans have been finalised.
“More parcel companies are now delivering later into the evening to meet changing customer needs, and we are redesigning our network to deal with growing numbers of parcels, including investing in two new Super Hubs.
“As part of our ongoing planning and negotiation, we are exploring a number of changes that would mean that we would still deliver letters by 5pm, as opposed to by 4pm currently.”