Britain's largest telecom companies have been directly warned by Washington against using Huawei equipment in their 5G networks, just hours after Vodafone admitted it had identified security flaws several years ago.

Vodafone, BT and Telefonica's O2, were summoned by US officials to a closed-door meeting at the US embassy in London on Tuesday to discuss the alleged risks posed by Huawei equipment to UK security.

Details of the meeting emerged after Vodafone revealed it had discovered hidden security flaws in Huawei equipment used on its Italian network about a decade ago. The telecoms giant said the vulnerabilities had since been resolved, according to Bloomberg.

The report said the security flaws, which date back to 2009, could have given Huawei unauthorised access to Italian homes and businesses. Vodafone rejected this.

The hastily scheduled meeting at the US embassy was thought to have been arranged with Robert Strayer, the US State Department's deputy assistant secretary for cyber. According to sources familiar with the matter, he was keen to reiterate US concerns over Huawei's equipment, which it claims can be used for Chinese spying.

Huawei has categorically denied the allegations. A statement said: "Singling out one vendor does nothing to help the industry identify and address cyber security threats more effectively."

The meeting follows revelations in the Telegraph last week that Theresa May had given the green light for Huawei to appear in parts of the upcoming 5G networks, against the wishes of the US government.