An ambitious project to replace the bespoke radio network used by ­hundreds of thousands of police, ­paramedics and fire crews with a cheaper system based on normal ­mobile signals faces a new delay of up to a year, ­according to Westminster sources.

The first users of the Emergency Services Network (ESN), a Home Office project involving BT’s mobile arm EE, Motorola and the consultancy KBR, are officially due to be connected in June next year.

The Sunday Telegraph understands however that the highly complex ­migration may not now begin until as much as a year later, potentially ­triggering hundreds of millions of pounds of extra costs to keep the existing system running longer.

Known as Airwave, it is due to be switched off in 2020. The full details of the delay are not yet clear but are likely to be laid bare when civil servants and executives are called to the Public Accounts Committee (PAC) in November. A hearing is being planned according to Westminster sources.

A spokesman for the committee declined to comment. The powerful group of MPs has already heavily criticised ESN for the Government’s failure to make contingency plans for delays. Motorola told the PAC that it will not be possible to keep Airwave up and running beyond March 2020, when Vodafone will scrap an old Cable & Wireless system on which it relies.