A trial of mobile signals on London's tube network is poised to begin on the Waterloo and City line, as authorities attempt to bring coverage Europe's biggest "not-spot".

The work is expected to be announced tomorrow by the Mayor of London Sadiq Khan as part of a package of measures designed to tout and improve the capital's digital connectivity.

It is understood that Transport for London (TfL) is working with the Chinese telecoms equipment manufacturer Huawei on the trial. Mobile operators will take it in turns to test their networks underground for a week, conducting engineering overnight and at the weekends when the Waterloo and City line is closed.

The trial has not yet begun and industry sources said preparations were making "slow progress". It is the latest of several attempts to introduce mobile coverage on the tube, all of which have failed for technical, commercial or logistical reasons.