Thousands of households across Britain may not receive their daily post until the evening under a major shake-up proposed by Royal Mail.
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" parcels to arrive at sorting offices.
But modelling of the changes has found this could mean more than 100 areas of Britain getting their post at 5pm or later, the Telegraph has revealed.
Of these, 17 areas may not get their post until 6pm at the earliest. North of the border, people in Kinross may have to wait until 7.30pm.
A Royal Mail spokeswoman told the Telegraph no final decisions had been taken.
Any changes 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.
'Outrageous' alterations
The union claimed the possible alterations 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 as well as 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.”
Royal Mail has given postal workers a 2% pay increase backdated to April 1 already, and is now offering the CWU a 3.5% 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 13% in October.
The CWU 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.
Royal Mail has repeatedly locked horns with the CWU over modernisation plans.