Malcolm Turnbull, the former Australian prime minister who banned Huawei from the country’s 5G network, has warned Theresa May the potential risks posed by the Chinese telecoms giants “cannot be effectively mitigated”.

In an interview with The Telegraph, Mr Turnbull said that Huawei was a “high-risk vendor” and it was not possible to “design a way around” security concerns associated with it.

Mr Turnbull, who attended Oxford University with Mrs May, said he had decided to ban the Chinese firms Huawei and ZTE from supplying 5G equipment last year after being warned by Australian intelligence it was “not possible” to find “engineering solutions” to mitigate the risk.

His intervention comes after this newspaper revealed last month that Theresa May had given the green light for Huawei to help build parts of the 5G network.

The disclosure has provoked heated debate both domestically and internationally, with the US warning that it risks harming intelligence sharing arrangements between the two counties.

Asked what advice he would give to the UK, Mr Turnbull said: “My view, the Australian Government’s view is that the UK has got to make its own decision.