Guests attending an event at the National Cyber Security Centre were left bemused after being told that they could access internal doors with the passcode "1234", according to reports.

       Diplomats and journalists were given the code as they arrived for a speech by Foreign Secretary Lord Cameron at the government organisation's high-tech headquarters, MailOnline reports.

       The NCSC is part of GCHQ, and advises ministers, the private sector and the public on hacking threats.

       Its remit includes providing the public with advice on coming up with passwords that can keep hackers at bay.

       Guidance the agency issued earlier this year cautioned people against having codes containing a "run of numbers", and warned that weak passwords leave internet users "vulnerable to attack."

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       "Research shows that weak passwords often contain names, places or a run of numbers," it said. "The more complex a password is, the more secure it becomes."

       The NCSC website also has a list of thousands of common passwords that should be "changed immediately" if in use, which specifically refers to the combination "1234."

       The agency has been approached for comment via email.

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       The Mail quoted a Whitehall source as saying the the NCSC has "robust and in-depth security measures in place" at its HQ.

       They suggested to the outlet that the visitors were issued would only give them access to non-sensitive parts of the building, such as toilets.

       Another source said: "It's the code they give to visiting journalists as it's all most of them can remember."

       "It won't let you roam the building," they added.