Things have moved on in the civil service since the days of Yes Minister. Back then senior civil servants remained the soul of discretion even after retirement. When Sir Arnold Robinson has advice to give to his successor, Sir Humphrey Appleby, he does it over lunch at a Pall Mall club.

Lord Macpherson, until recently the Treasury’s top mandarin, has some advice for the current government: it’s time to move on from quantitative easing, the scheme that has been pumping electronic money into the economy since early 2009.

Not for Macpherson a quiet word over an agreeable bottle of claret. Instead, he took to Twitter to compare QE to heroin: ever bigger doses are needed to get a high.

Did Macpherson say this when he was working for Alastair Darling, who originally gave the Bank of England permission to start QE, or George Osborne, who said the economy needed more of it? We won’t know that until the records of the Great Recession and its aftermath are released in a couple of decades, but if he did the warning was not heeded.

The best that can be said for QE is that it helped prevent an even deeper slump in the winter of 2008-09 but was of less importance than the re-capitalisation of the banks and the deep, co-ordinated cuts in interest rates from central banks.

There were also better ways to boost demand. To an extent QE merely compensated for the fiscal austerity announced by Osborne (and strongly supported by Macpherson). What’s more, much of the extra money swilling around the economy found its way into speculation rather than into remedying the economy’s structural weaknesses. Rich people benefited because the value of their homes and share portfolios went up; poor people suffered because commodity prices also went up, raising food and fuel prices.

So Macpherson is right. QE was never particularly effective, was always fundamentally inequitable and has been left in place for too long. Central banks know this, which is why the US Federal Reserve will soon starting selling bonds and why the financial markets will be all agog for any hints from Mario Draghi at this week’s Jackson Hole get-together about when the European Central Bank might do the same.

The issue is not whether central banks should wean themselves off QE but whether they can do so without bringing to an end the tepid recovery in the global economy. Macpherson’s tweet was in response to a warning by Rupert Harrison, Osborne’s chief economic adviser, that the ECB risked a “car crash” if it abandoned QE too quickly. When you are hooked it can awfully hard to kick the habit.

Can Trump make US debt great again?

In the past couple of months Donald Trump has tried and failed to repeal Barack Obama’s Affordable Health Care Act, threatened North Korea with war, fired the opening salvos in a trade war with China and lost the confidence of those running America’s big corporations.

Since this catalogue of misfortune seems to have had zero impact on Wall Street, it is worth contemplating what might shake the markets out of their complacency. How about the government running out of money and repudiating its debts?

The US Treasury hit the borrowing limit set by Congress in March and has since been unable to issue any new debt. It has been making ends meet since by running down its reserves but you can only live off fat for so long and the cash will be used up by mid-October.

On the assumption that the US won’t want to leave it until a minute to midnight to sort things out, the debt ceiling will need to be raised within the next few weeks. That’s cutting things fine, especially since some Republicans in the House of Representatives are insisting that raising the ceiling should be contingent on public spending cuts and that will mean a real struggle to get the necessary bipartisan support in the Senate.

There are two ways the issue could be resolved. Trump could use his authority to prod Congress into raising the ceiling. Or a run on shares caused by fears of a default could concentrate minds. Given that Trump has no authority, the latter is favourite.