A replacement for how Britain’s emergency services communicate is set to go over budget by at least £3.1bn, a spending watchdog has warned.

The Home Office has already delayed switching off the existing system by three years to 2022.

But the National Audit Office (NAO) has raised doubts about whether the project will be ready by then.

Ministers say the new service would result in faster response times and better treatment.

The Emergency Services Network (ESN) would replace Airwave, a digital radio network introduced in 2000 and used by all 107 police, fire and ambulance services in England, Scotland and Wales.