Emergency services could lose vital phone signal in parts of London if a new communications system costing over a billion pounds is rolled out, it is feared.

The Home Office is working to replace the current network, a radio-based system the police, ambulance and fire services use to communicate with each other.

Under the new system, they will communicate using mobile data – 4G, on EE.

It will include the “push to talk scheme” allowing them to use their mobile phones like walkie talkies.

But concerns were raised at a London Assembly meeting yesterday that workers might not be able to get signal everywhere under the new system, which would mean losing vital contact in critical situations.

Bryan Cook, programme director for the emergency services mobile communications at the Home Office, said: “We can’t promise blanket universal coverage everywhere and a lot of people are concerned about there being good signal everywhere.

“We need to look if there are any places not covered by the EE contract and see how we can cover those places.”

EE’s mobile data network gets signal in around 99 per cent of the capital but there is no guarantee it will reach every area– especially the London Underground.

Assembly members also raised concerns there is not an official date for when the new system will be fully installed – the first phases of the project will begin in 2019.

Mr Cook said: “Although we don’t have a strong track record with delivery.

“This is a world first project and there are uncertainties. We know how to do the technical work behind the project but it’s about adopting that technical work.

“Emergency services will start using the new system in non-critical situations and then use it in a series of stages.”

He also raised uncertainties about whether the project would cost £1.1 billion as per the Home Office’s original guidelines, or whether it could grow more expensive over time.

He added said: “We recognise that if more information about how we can run and manage the project becomes available it may become more expensive.”

He failed to how much these costs would increase by and who would pay for them as well as if the Home Office paying any additional funding.