All four firms are adapting to diminished traffic in letters and important documents because of e-mail, and the growing demand for parcel delivery to end-consumers generated by e-commerce sites such as Amazon.

ECONOMIST: Global express-package companies

As a result of all this, and the boom in e-commerce, the big parcel companies, such as Federal Express, UPS and DHL (not targets of the current investigation), have seen business boom.

ECONOMIST: Inspecting the cargo | The

In addition to its traditional services of letter and parcel delivery, the Post Office now provides services such as e-commerce fulfilment, billing and customer management, logistics and warehousing.

BBC: UK Post Office name change