#600 2011 · UK Behavioural Insights Team / HM Revenue & Customs · Government / tax collection
Telling late taxpayers that almost everyone else already paid moved £2.4 million in three weeks, with no threat, fine or new enforcement
the problem
The obvious lever for getting people to comply with a rule (threaten a bigger penalty) is also the most expensive and adversarial one to pull
background
HM Revenue & Customs sent the same standard reminder letter to taxpayers who had declared but not yet paid their tax bill for years, essentially restating the amount owed and the consequences of nonpayment, with response rates that had plateaued — the default lever tax authorities reach for to improve on-time payment is escalating threat: bigger fines, more explicit enforcement language, faster referral to collections.
The UK Cabinet Office's Behavioural Insights Team, established in 2010 and popularly known as the 'Nudge Unit,' set out to test something different with HMRC: rather than making the penalty more frightening, tell taxpayers an accurate fact about what their peers were actually doing, on the theory that people calibrate their own compliance partly against a belief about how many others are complying.
what everyone would do
The default lever any tax authority reaches for to improve on-time payment is escalating threat — bigger fines, more explicit enforcement language, faster referral to collections — and HMRC's own standard reminder letters had done exactly that kind of restate-the-penalty messaging for years, with response rates that had plateaued.
what they saw
The Behavioural Insights Team saw that late payers weren't necessarily unaware of the penalty, since the standard letter already stated it — they were likely miscalibrated about how many people like them were actually paying on time. Correcting that mistaken belief with an accurate, specific social-norm statement could move behavior more than making an already-known threat bigger.
the move
Around 100,000 taxpayers who owed declared but unpaid tax were randomized across several reminder-letter variants, the most effective of which added a specific social-norm statement — that the great majority of people in the recipient's own local area or town had already paid their tax on time — rather than repeating the amount owed or the penalty for nonpayment. No fine was increased, no new enforcement mechanism was introduced; the only change was one added sentence stating an accurate local norm.
why it works
Adding one sentence stating that the great majority of people in the recipient's own local area had already paid on time corrects a taxpayer's likely assumption that late payment is more common or more socially acceptable than it actually is, and because people calibrate their own compliance partly against a belief about what their peers are doing, correcting that belief shifts what feels normal and expected. The more locally specific and identity-relevant the reference group cited — a home town rather than the country as a whole — the stronger the identification and the larger the effect, which is exactly the gradient the trial found across message variants. Because the change cost nothing beyond one sentence of copy and required no new enforcement infrastructure or fine increase, the £2.4 million pulled forward in 23 days vastly outweighed the cost of testing and deploying it.
the payoff
Payment rates rose from roughly 67.5% in the standard-letter control group to as high as about 83% with the most localized 'home town' norm message — pulling forward an estimated £2.4 million in tax payments within a 23-day trial window, with the Behavioural Insights Team projecting the approach could advance roughly £160 million of tax debt collection over a six-week period if applied at scale.
where it breaks
The mechanism depends on the true norm actually favoring compliance and the recipient not already knowing it — if most people genuinely weren't paying on time, stating the accurate norm would backfire by confirming and normalizing the very behavior the letter was trying to discourage, a well-documented risk in social-norm messaging (anti-littering campaigns that stated high litter rates have inadvertently increased littering). It also depends on the audience actually identifying with the specific reference group cited; a norm framed around a group the recipient doesn't feel part of carries little persuasive weight. And the effect doesn't necessarily transfer to compliance failures where the binding constraint is capacity rather than willingness — a taxpayer who genuinely cannot afford to pay isn't moved by a norm message regardless of how socially uncomfortable falling behind might feel.
what came after
The HMRC tax-letter trial became one of the most cited proof-of-concept studies for the UK's Behavioural Insights Team and for social-norm messaging in public policy generally, published in peer-reviewed economics research (including a study titled 'The Behavioralist as Tax Collector') and replicated in various forms by other tax authorities and government behavioral-science units internationally.
references
- [1]The Behavioralist as Tax Collector: Using Natural Field Experiments to Enhance Tax Compliance (NBER Working Paper 20007)National Bureau of Economic Research, 2014nber.org
- [2]Behavioural science nudges can stop tax avoidanceWarwick Business School, 2017wbs.ac.uk