The Booksellers Association (BA) said that Amazon already had a ‘de facto monopoly’ and urged its members to write to the OFT before its inquiry closes on 18 July.

Chief executive Tim Godfray said: "Our members are facing huge competition from internet traders and this proposed acquisition potentially puts an already dominant player into an even stronger position."

He added that high street retailers could not survive indefinitely as ‘showrooms’ for internet booksellers.

The BA is to make a formal submission to the OFT opposing the proposed acquisition and the Publishers Association is expected to follow suit.

A book printer, who did not want to be named, said that the merging of the two internet retailers could help shift the book printing industry further towards a print-on-demand model.

Amazon, which has 70% share of the UK online book market, has its own print-on-demand service, called Createspace, which was formerly known as Booksurge.

Amazon has been accused by US print-on-demand publishers of trying to force them to pay Amazon to print its books or have the ‘buy it now’ button removed from its website.

The retailer has declined to say why it has acquired The Book Depository, which is estimated to have a turnover of around £120m, or how much it paid. Industry experts, including Philip Downer, former chief executive of Borders, have speculated that it may be because The Book Depository, which supplies more than 100 countries, has a global reach whereas Amazon operates in certain territories.