Peter Costello is back in the news, with an internet-based poll from Essential Media showing public opinion to be divided on his future: 34% say he should resign, 46% that he should stay in parliament (but with no consensus on what capacity), and 20% are undecided.

I’ve been thinking about the Costello question for a while — especially since Alex Mitchell last week made a brave prediction that he would return to the leadership — and I’ve finally worked out the appropriate historical analogy. It’s an unlikely one, but bear with me: Costello reminds me of Mary, Queen of Scots.

Recall some history: Mary Stuart, widow of the French king and queen of Scotland in her own right, was also the next heir by blood to Elizabeth I of England, and in the eyes of many Catholics the rightful queen of England. For England’s Protestant political class, her succession represented their worst nightmare, with the likely reversal of the country’s religious and foreign policies.

Accordingly, Elizabeth’s ministers worked tirelessly to dispose of Mary: they lobbied against recognising her as heir presumptive, they intrigued with her enemies in Scotland to have her deposed, and when she was a fugitive in England they pressed Elizabeth to keep her imprisoned and ultimately to have her executed.

But at the same time, they were conscious of the fact that things could go wrong, Elizabeth could die at any time, and Mary might well end up as their queen — so they maintained a constant unofficial stream of messages to Mary, assuring her of their good intentions and their secret loyalty to her interests.

That’s how monarchy works. Hereditary succession is capricious, and those who depend on the monarch’s favour always have to keep one eye on the succession. Similarly, William III’s ministers kept up a treasonable correspondence with the Jacobite court in the 1690s, and the Hanoverian kings always found their sons to be competing centres of political influence.

Now, in the semi-monarchical environment of the Liberal Party, its MPs find themselves in the same position as Queen Elizabeth’s ministers.

They would dearly like to be rid of Costello; they don’t want and don’t expect him to take the leadership. But they know that it might happen regardless, through failure of the alternatives, and so they have an incentive to stay in his good books just in case.

Hence the hopelessly mixed messages coming out of the parliamentary Liberal Party. Even those who are most strongly against a Costello succession know that their careers may one day be in his hands. So double-dealing becomes a way of life, and people’s private positions contrast sharply with their public ones.

We know how Mary Stuart’s story ended: she went to the block, and Elizabeth and most of her ministers died peacefully in their beds. But it would be unwise to count on history repeating itself.