The lights are going off in Europe. In Greece, it's called "operation thermostat." In Holland, the motto is "zet de knop om" - turn down the knob. Germany has plunged its public monuments into darkness and enforced cold showers at swimming pools.

The goal is to save energy. Gas prices in Europe have hit an all-time high. Next month, UK bills will be almost triple their level last winter. Money expert Martin Lewis warns, "people will die this winter," unable to heat their homes.

The UK government insists energy use is a "decision for individuals," and they will not force people to unplug and switch off. However, chancellor of the ExchequerThe chancellor of the Exchequer, often just called the chancellor, is the UK government's chief finance minister. They are in charge of taxation and government spending and borrowing. Nadhim Zahawi said last Friday, "we should all look at our energy consumption".

According to research, UK households can follow energy-saving tips to cut their gas bill by 31%. Media and charities are offering advice, from blocking draughts to swapping shower heads.

Gently persuading people to make better choices is the big idea behind behavioural economics - using psychology to understand decision-making. Governments have embraced the theory, setting up nudge unitsThe first was set up by the UK government in 2010 and is called the Behavioural Insights Team. Since then, over 200 institutions globally have applied behavioural insights to public policy. and employing psychologists to develop policies.

But does it work? New research is turning former fans into its biggest critics. Some say nudge theory is even worse than useless.

Supporters say the power of the nudge is enormous. For example, if you have to opt-in to an organ donation scheme, only about 30% of people do. In countries where you must actively opt-out, 85-90% are automatically enrolled. A simple nudge makes organ donation the norm.

Other techniques include simplifying choices, applying social pressure¹, displaying health warnings, and offering reminders².

A nudge campaign to persuade everyone to turn down their thermostat from 20C to 18C would save 14% on gas bills. Shorter showers with a low-flow shower head could cut another four per cent. Households could shave off a further 3-6% by turning the heating off in September and March.

But nudge theory is on shaky ground, says psychologist Magda Osman. A recent review of 212 studies found "no evidence" that nudging worked. Its effect is no greater than a placeboPatients may report feeling better after taking treatments with no medical value. This is called the placebo effect. In order to distinguish between perceived and actual effects of a new treatment, researchers will test a placebo or "sham" alongside the real treatment - and compare the results. or statistical noiseUnexplained variations in real-life experiments.. Supporters have cherry-picked successful projects, ignoring those that failed.

Scientists Nick Chater and George Loewenstein once believed nudges could solve social problems. But they now doubt its power, writing that "human progress" requires system-wide change. We need more than "hints and tips to survive in a hostile world".

One energy boss predicts that half of UK households will be in fuel povertyWhen a household spends more than 10% of their income on heating or is unable to afford to adequately heat their home. by January. So many demand radical action instead of energy-saving tips.

Half a million have signed up to the campaign Enough is Enough³, demanding price cuts and increased benefits. The package may cost £100bn a year. Over 100,000 have pledged to stop paying their bills altogether on 1 October.

A bleak winter may decide whether individual behaviour or collective action can solve the world's energy crisis.

Yes: Behavioural economics shows us that if millions of people change their habits it can have an enormous impact on society. And change is infectious - the more we see it, the more we want to change too.

No: It is easy for governments to tell individuals to use less energy. But when families cannot afford to heat their homes through the winter, they need financial help, not tips and tricks.

Or... In reality, we need to change the system and individual behaviour - at the same time. In a fair society, everyone behaves responsibly and there is support for those who need it.