At present the White Pages are delivered automatically unless a customer opts out, but most people now use other means to look up phone numbers, mainly online. However, only 51,000 of the 3.7 million who receive the White Pages decided to opt out, despite surveys carried out in Mol, Stabroek and Aartselaar which suggested that only 3% of people found the paper version useful.

But demand had been falling: in the year 2000 about five million books were printed, and now only 3.7 million. But that was a result of an improvement in distribution methods and a reduction in the number of landline subscribers. A change to printing techniques brought a reduction in the amount of paper used, from 13,000 tonnes in 2007 to 8,000 tonnes in 2009.

The telephone book is produced and distributed by Truvo, formerly known as Promedia, with the agreement that it also produces the Yellow Pages, which brings in advertising revenue. However, as in other sectors of the media, advertising revenue in the Yellow Pages is falling as people use it less and less.

Rather than full-page ads from large companies, Truvo’s main source of income was the small box-ads placed in the Yellow Pages by local businesses – exactly those hardest hit by the economic crisis. The White Pages is produced in 19 regional editions and contains in all over six million numbers.

The switch from opt-out to opt-in, which Van Quickenborne announced on his Twitter feed, will, he said, save the equivalent of 38,000 trees and cut CO2 emissions by 1,512 tonnes – the same as the daily footprint of 476,280 families.