The joint operation, by Royal Mail and Skyports Drone Services, will initially operate on the islands for three months.

It will see letters and parcels transported from a delivery office in Kirkwall to Stromness, from where drones will take them to staff on Graemsay and Hoy to carry out their usual rounds.

The drones, a Speedbird Aero DLV-2 model, can carry payloads of up to 6kg.

It's hoped it will significantly improve service levels and delivery times to the two islands, as the often challenging geography and weather can cause disruption and pose safety risks to postal workers.

Chris Paxton, head of drone trials at Royal Mail, said the fully electric unmanned aircraft would also assist the company's efforts to reduce its carbon emissions.

Should it prove effective, the so-called Orkney I-Port operation could be continued on a permanent basis.

The project has been funded by the Department for Transport's Freight Innovation Fund.

Plans for a Royal Mail drone delivery service were first detailed last year, with the firm saying it aimed to eventually bring the technology to all corners of the UK.

Other delivery companies have also been trialling post by air, notably Amazon in parts of the US.