The cabinet secretary has circulated a memo dating from 1974 on plans for a hung Parliament, according to newspaper reports.

The document, seen by the Guardian and written by the then-principal private secretary to prime minister Edward Heath, Robert Armstrong – who later served as cabinet secretary himself – details options for senior government and Buckingham Palace officials if a general election failed to produce an obvious government.

The memo acknowledges that the monarch may be placed in a delicate constitutional position, as after the election of 1974, Edward Heath remained in office for the weekend after the election, attempting to form a coalition with the Liberals – despite having fewer seats than Labour.

If that example were followed, Gordon Brown would be allowed to attempt to form a government if the Tories fail to win an overall majority of seats.

Another option detailed in the Armstrong note is that the Queen could invite a figure other than one of the party leaders to form a government.

In the event of a hung Parliament after the election – expected to occur on May 6 – the management of a transition would fall to the triumvirate of cabinet secretary Sir Gus O’Donnell, No 10 permanent secretary Jeremy Heywood, and the Queen’s private secretary Christopher Geidt.