The company said 1,400 of the new postboxes would be installed across the country in more than 30 locations over a six-month period, starting in August.

Locations will include Aberdeen, Belfast, Birmingham, Cardiff and Leeds.

Customers will be able to post parcels in the same way that they currently post a letter, provided that postage has been pre-paid using Royal Mail's own online labelling service.

Existing letter postboxes were introduced in the 1850s and Royal Mail said the new move represented the first major change in the system since then.

"The launch of parcel postboxes is also one of the biggest innovations in parcels since the launch of Parcel Post in 1883," it added.

The rollout follows a successful trial of the idea last year.

Royal Mail will be converting existing meter boxes, which it said had a larger aperture and a secure design.

Mark Street, head of campaigns at Royal Mail, said: "We hope that the wider roll-out gives added flexibility to online sellers who might be running a business in their spare time and not keeping regular office hours."

People will also be able to return parcels using the system, as long as they have a Royal Mail barcode attached.

The full list of locations is:

• Leeds
• Newcastle & Tyneside
• Sheffield
• Warrington
• Swindon
• Nottingham
• Romford
• Manchester
• Preston
• London Central
• Birmingham
• Chelmsford
• Chester
• Greenford
• Glasgow
• Edinburgh
• Bristol
• Croydon
• Poole
• Aberdeen
• Southampton
• Belfast
• Peterborough
• Plymouth
• Cardiff
• Norwich
• Swansea
• Bournemouth
• Exeter
• Truro
• Inverness
• Carlisle