A copy of the document from the National Cyber Security Centre (NCSC) - part of GCHQ - was obtained by technology website Motherboard and a BBC follow up found it was legit.

The NCSC report specifically discusses the threat to the energy and manufacturing sectors. It cites connections from multiple UK internet addresses to systems associated with "advanced state-sponsored hostile threat actors" as evidence of hackers targeting energy and manufacturing organisations.

The document said NCSC believes that due to the use of widespread targeting by the attacker, a number of industrial control system engineering and services organisations are likely to have been compromised.

An NCSC spokesman said that it was aware of reports of malicious cyber-activity targeting the energy sector around the globe. "We are liaising with our counterparts to better understand the threat and continue to manage any risks to the UK."

Russian hackers have also affected Ireland's Electricity Supply Board (ESB), according to a report in the Times on 15 July in what appeared to be a test of the software. Industrial control systems at ESB were implicated, which could mean parts of the electricity grid in Northern Ireland were made vulnerable.