Solar-powered postboxes with an extra-large slot for parcels are being trialled by Royal Mail.
The firm says it is the biggest change to the design of the red postbox since its introduction more than 175 years ago.
Five postboxes are currently being piloted – one in Fowlmere in Cambridgeshire, and four in Hertfordshire, in Letchworth, Hertford, and two in Ware.
They have been retrofitted with solar panels, which power a camera that is used to scan a barcode on the parcel. That opens a separate chute for the package to be dropped in.
Letters can still be posted in the usual way through a separate opening. Proof of posting is also available via an app.
Royal Mail said it is responding to the rising popularity of online marketplaces, where people can sell unwanted items, as well as shoppers sending returns.
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Currently, postboxes – of which there are 115,000 in the UK – are able to accept small parcels.
But Royal Mail said in a statement that “thousands could be adapted to the new design to accept larger parcels”.
Emma Gilthorpe, Royal Mail’s chief executive, described the upgrade as a “historic change to our postboxes”.
“In an era where letter volumes continue to decline and parcels are booming, we are giving our iconic postboxes a new lease of life on street corners across the nation.”
Commenting on the business case for the upgrades, Royal Mail told Sky News: “It makes sense to utilise them [postboxes] to make sending parcels more convenient and make our postboxes more useful for the modern Royal Mail customer.”