UK spy agency GCHQ’s cyber security arm, CESG, was left without PGP encryption for more than four months, according to a government report.

This "prevent[ed] direct electronic receipt of evaluation reports", it emerged in the Huawei Cyber Security Evaluation Centre (HCSEC) Oversight Board (PDF) annual report.

“Internal processes were updated to ensure this issue does not recur,” said the report.

Meanwhile the report, intended to assess the perceived risks arising from the involvement of Huawei in parts of the UK’s critical national infrastructure, once again gave the Chinese kit-maker the green light.

Any risks to UK national security from Huawei’s involvement in the UK’s critical networks have been sufficiently mitigated, found the third annual probe from the HCSEC Oversight Board.

However, the report found the board had failed to verify Huawei’s source code. It said HCSEC has “provided less than ideal assurance to the operators, as part of their risk management regimes”.

It said: “The incomplete delivery of source code obviously means that HCSEC cannot provide assurance or risk management artefacts for the additional code.

"While this is a matter of significant concern, the [National Cyber Security Centre] does not believe this process is in any way malicious, but is based solely on Huawei supplying source code for the features procured and used by UK operators.

“This opinion is based on a targeted analysis of previously received source code and corresponding binary.”

Huawei has effectively been banned from bidding for US government contracts because of concerns over espionage.

However, the Chinese company has been working with the UK government for some time. Over the last five years, Huawei has invested £1.3bn expanding its operations in the UK. ®