The White House has stepped up warnings to the UK about allowing Huawei into its 5G telecommunications networks, saying that any such move would pose a risk to MI5 and MI6, the British secret intelligence services.

Robert O’Brien, the US national security adviser, told the Financial Times that any UK government decision to allow the Chinese telecoms company to participate in the country’s ultrafast 5G networks risked giving the Chinese Communist party access to the “most intimate” details of British citizens and the ability to steal national secrets.

“They are just going to steal wholesale state secrets, whether they are the UK’s nuclear secrets or secrets from MI6 or MI5,” Mr O’Brien said in an interview. “It is somewhat shocking to us that folks in the UK would look at Huawei as some sort of a commercial decision. 5G is a national security decision.”

Washington has repeatedly urged the UK to completely ban Huawei, but the warning from Mr O’Brien raises that pressure to a new level. It comes as Prime Minister Boris Johnson prepares to decide whether to ban Huawei from the country’s 5G networks.British security officials last year concluded that any risk from Huawei can be mitigated if it is barred from the network “core”, but US officials disagree with that assessment. Australia has also urged the UK to exclude Huawei from its 5G networks.

One reason Britain faces such pressure is because it is one of the “Five Eyes” partners — with the US, Canada, Australia and New Zealand — that share critical intelligence. The US has previously said allowing Huawei in 5G networks could limit intelligence sharing.

In a stark warning about the threat to individuals’ data, Mr O’Brien said China would be able to “micro-target” individuals to “exploit their hopes and their fears” by gaining access to personal details. US concerns about 5G had been amplified by what he said were growing Chinese efforts to obtain the genetic data of people around the world.

US security agencies have in recent years boosted their focus on Chinese investment in US biotech companies and the hacking of patient data from hospitals and laboratories.

“If you get all the information on a person and then you get their genome, and you marry those two things up, and you have an authoritarian state wielding that information, that is an incredible amount of power,” Mr O’Brien said. “Why the UK would sign up for such a programme is astonishing.”