George Bernard Shaw, it is said, once met an actress and asked her: "would you sleep with me for a million pounds?" "I would think about it" she replied. "Would you sleep with me for a pound?" he then asked. "No" she replied. "What sort of woman do you think I am?" He replied: "We've established that, madam. Now we are haggling about the price."

We should thing about policies the same way. Sometimes, it is worth establishing the principle, and then haggle about magnitudes and timing.

For example, New Labour introduced the minimum wage at a derisorily low rate in 1999. But having established the principle of a minimum it was easy to raise it, and so the UK's minimum is now comparable to those of many other nations. Similarly, Thatcher's privatizations began as a small-scale attempt to reduce government borrowing, but they quickly scaled up. In the same vein, this is why so many of us on the left have zero tolerance for racist or anti-immigration rhetoric and why we were repulsed by Ed Miliband's "controls on immigration" mug. Once such discourse becomes acceptable, it leads to the hostile environment policy and the Windrush disgrace.

It's from this perspective that we should regard debates about the policy response to Covid-19. It's an opportunity to "establish that, madam" - to create a consensus for policy principles which we can expand or refine later.

In the case of fiscal policy, this has already happened. In borrowing to subsidize wages among other things, Rishi Sunak has established that the UK has abundant fiscal space and that the notion that there is a binding limit on the "nation's credit card" is nonsense. As Eric says, austerity was a "fraud."

Similarly, Spain is introducing something like a basic income. Whilst purists might worry that it is not as universal or unconditional as a true UBI, I'm not sure this much matters for now, What does matter is establishing the principle. Once a policy is in place, even in mild form, we have overcome a huge obstacle - the status quo bias. It is much easier to reform than to introduce.

A lot else, though is up for grabs. One reason why so many Germans are opposed to the idea of coronabonds is that they would establish the principle of a euro-wide backed bond and so be a stepping stone to a fuller fiscal union and to fiscal transfers. Which of course is why so many others are pushing the idea.

Also, one thing this crisis has taught us is that we need in place the infrastructure to give support to people quickly. In this regard, whilst the current depression is almost unprecedented in speed and severity, it is not unprecedented in being unpredictable. As Prakash Loungani has shown, mainstream economists and policy-makers have failed to foresee almost all recessions. Which means that monetary and fiscal policies which operate on demand with a lag are insufficient: they might moderate the downturn and accelerate the upturn, but they can't prevent the downturn. Hence the need for automatic stabilizers.

What I'm arguing for here is to seize the moment, to use this crisis to establish policies and institutions that are hard to reverse. Many of you think this crisis will change public opinion in favour of redistribution and greater public spending. I've no such confidence. We tend to project (pdf) our current preferences too much into the future and fail to see that they'll change. We cannot, then, rely upon the public mood staying as it is.

In this sense, I've mixed feelings about Frances' claim that now is not the time for a universal basic income or helicopter money. She might be right speaking of them as technical fixes, but now is the time to establish the case for them in principle, and to lay down the plumbing to enable them to work - such as, for example, ensuring that everybody has a bank account.

Much of what I'm saying here might seem obvious, even cliched. "Thin end of the wedge" and "slippery slope" have long been conservative objections to mild social reform.

But I'm not sure it is. What I'm saying here contradicts some common views of policies. Technocrats see them as fixes of current problems whilst some naïve leftists always complain of their inadequacy. What both perspectives miss is that policy-making is not merely an engineering matter of pulling levers and fixing things. Even apparently mild policies can lead to bigger things.

We must always ask, therefore of any policy: where will this lead? Sometimes, it opens a door to further change - as with the NMW. At other times, though, it can be a dead end. New Labour's increases in public spending died with its electoral defeat, whilst its embrace of new public management (pdf) alienated many traditional Labour supporters and failed to increase public sector productivity.

But of course, policy doesn't merely change the intellectual climate. It also changes the material base of support for future policy change. Thatcher, for example, both destroyed the unions and - via expanding the financial sector and selling off council housing - enlarged the client base for financialization. And in expanding universities, New Labour expanded the cohort of immaterial labour with a globalist outlook: it was Blair who laid the foundations for Corbyn.

My point here is a simple one that's often overlooked. Policy-making is a dynamic, not a static process. It is not merely a matter of getting the right technocratic fixes.