The Trial as Verdict: How 'What Works' Became Britain's Way of Not Deciding

Somewhere in Whitehall, a policy is being tested. There is a control group, a treatment group, a protocol, a pre-registered hypothesis and a peer-reviewed evaluation. By every metric the policy is rigorous. What it is not is political — and this is precisely the problem.

The United Kingdom has spent the past fifteen years building an apparatus around the idea that government should do "what works". The What Works Centres, the Behavioural Insights framework, the proliferation of randomised controlled trials across public services, the Treasury's insistence on business cases and evaluation strategies — all of it rests on an admirable premise: that public money should be spent on things that demonstrably help.

But there is a second premise, less often stated. If evidence determines what works, then the question of what we want becomes redundant. Value conflicts are quietly reclassified as data gaps. Voters are invited to admire the rigour and stop asking what the policy is for.

The Question Behind the Question

Consider a familiar example. A pilot scheme improves a service; the evaluation finds a measurable effect; the scheme is rolled out. What was the scheme actually for? Improvement in what, according to whom, at what cost, and with what trade-offs?

Randomised trials are excellent at answering narrow, well-specified questions. They are much less effective at handling the things that actually divide the public: liberty against security, speed against safety, efficiency against equity, local control against national standards. These are not empirical disputes to be settled by evidence. They are choices about priorities, and they require politics.

The What Works architecture does not ignore these questions so much as tunnel beneath them. Once a policy question has been framed as "does X work?", the argument has already narrowed. The framing itself has taken a position on what counts as working. And the answer, when it arrives with confidence intervals attached, arrives with a political authority it has not earned.

The Hive of Experts

There is a shape to this. A hive is a place of coordinated effort under a single logic — and Britain's evidence ecosystem has developed something like that logic. Funders ask for impact. Researchers deliver measurable findings. Departments cite trials. Ministers praise the evidence. Journalists report the numbers. The rotation is smooth, and it rewards fluency in the right vocabulary.

The consequence is that a set of values is smuggled in through methodology. A trial that measures employment outcomes but not dignity, that measures cost-saving but not access, that measures attendance but not attention, has decided in advance what matters. Those decisions are rarely declared. They appear instead as technical choices, made by people who are not accountable for them and whose names often do not appear in the final policy document.

This is not an argument against expertise. Competence in public administration is badly needed and too often absent. But expertise is not the same as authority. An epidemiologist can tell you the likely transmission effects of a policy. She cannot tell you whether the policy is just. That question belongs to the public, and the public has been asked to step aside while the modelling is completed.

The Treasury's Quiet Constitution

The Green Book and its associated guidance deserve particular attention. These documents — technical, cautious, full of discount rates and optimism bias — have become something like a constitution for British public spending. They determine which projects get approved, which outcomes count, and whose benefits are valued.

That is a remarkable arrangement in a democracy. A set of methodological conventions, refined over decades by officials and economists, effectively presides over the distribution of public resources. The conventions are not neutral. They privilege measurable benefits over diffuse ones, short-term returns over long-term transformation, and central calculability over local knowledge. They are defensible choices. But they are choices, and they should be debated as such.

A Defence of Evidence Pluralism

The alternative is not to abandon evidence. It is to insist on pluralism. Let trials run; let them be rigorous; but let them sit alongside other ways of knowing — local testimony, professional judgment, historical experience, philosophical argument about what a good service looks like. The point is not to flatten these into a hierarchy in which the number always beats the narrative. It is to recognise that a decent polity uses many instruments.

There is a strong case for a more transparent politics of evidence. Ministers should be required to state, in plain language, the values that underpin their targets. Evaluations should be asked to report what they did not measure and why. Departments should be encouraged to say openly that a decision rests on a judgment of priorities, not only on a finding of fact.

Above all, the questions that belong to voters should be returned to them. If a service is to be reorganised, that is a political act, not a technical consequence. If a road is to be built, that is an argument about what kind of country we live in. If a benefit is to be capped, the pain and the saving are matters for public deliberation, whatever the cost-benefit ratio says.

The evidence cult has given Britain a great deal of competence and a little too much silence. It has produced better evaluation reports and weaker arguments. It has made it harder for ministers to lie about facts, which is a genuine gain, and easier for them to avoid the questions that don't have facts attached — which is a considerable loss.

Politics Is the Point

A government that will only act when the evidence is conclusive will not act on many of the things that matter most. Innovation, redistribution, institutional reform, cultural renewal — none of these comes with a trial design that could generate a clean answer. The demand for certainty becomes an excuse for inaction, and the willingness to make a judgment in the face of uncertainty becomes the essence of democratic leadership.

The What Works movement was born out of impatience with ideology dressed as fact. It has become the opposite: a system in which technical authority displaces political choice, and the public is invited to spectate. The hive should be opened. The argument is the work of self-government, not a distraction from it.