The Chinese state could cut off cars and household appliances from Britain's 5G network if the country's telecoms giant is allowed to help build the system, according to a former government security adviser.

Peter Varnish, who was a senior Ministry of Defence official, suggested a decision by Theresa May to allow Huawei to help build even limited parts of the network such as antennas and other “non-core” infrastructure, could allow Beijing to "shut down" signals to vehicles and everyday objects.

In a report due to be published this week, Dr Varnish warns that a manufacturer could "interfere" with antenna designs and even block or divert signals away from individual devices.

The report, by the Henry Jackson Society think tank, comes after Mike Pompeo, the US Secretary of State, became the latest figure to attack a decision by the National Security Council, which is chaired by Mrs May, to give Huawei access to the country's 5G network.

The Trump administration has been lobbying European countries against allowing Huawei access to 5G networks, fearing that the Chinese government would have unrestricted access to information streams handled by the company.

Huawei is a private firm and China has insisted that banning its involvement in the 5G network would amount to protectionism.