Royal Mail said the changes would ensure it was able to maintain its estate of 115,000 postboxes, despite a 33 per cent drop in volumes since 2005.
Between 45,000 and 50,000 of its postboxes will move to the earlier collection time – typically 9am to 3pm – although the company has pledged there will still be a late posting box within half a mile.
It has also said it will introduce 2,000 new boxes in areas of under-provision, particularly in rural parts of Scotland and Northern Ireland. Some of the new boxes will also be added in popular areas such as train stations and shopping centres.
About 12,000 postboxes in rural areas are already emptied through collection on delivery, but the majority of those affected by the changes will be in urban and suburban areas. An indicator tab on the postbox will show if the collection has been made.
Royal Mail said the changes would unlock the opportunity for efficiency savings, while adding that many postboxes no longer covered their costs.
A spokesman said: “Rather than decommission uneconomic postboxes, while staying within the regulated density requirement, Royal Mail will ensure their viability by improving the efficiency of its collections arrangements.”
The company said it has discussed its plans with Citizens Advice and Consumer Council Northern Ireland and has also notified Ofcom.
The regulator requires that 98 per cent of all households should be within half a mile of a postbox.