FOR all the National Health Service's hard work to boost organ donation, around 1,000 people die each year for lack of a transplant. The active waiting list numbers more than 7,600, and 10,000 may be a fairer reflection of need. As hypertension, obesity and the miracles of modern medicine proliferate, that gap is likely to increase—unless donation rates rise dramatically. Deceased donors are twice as numerous in Spain as in Britain, per million people (see chart). Even the EU average is higher. (Britain does better when living donors are included, but dead ones are more useful because they can part with a wider range of organs.) Why the difference?

For many the answer lies in Britain's “opt-in” regime of informed consent. A potential donor has to signal his intent by enrolling on an official Organ Donor Register. Though 90% of Britons say they approve of donation, only 30% have signed up. Spain, and most EU members, have instead embraced some form of presumed consent, in which everyone is assumed to be a donor unless he expressly “opts out”. This week the British Medical Association (BMA), which represents doctors, urged switching systems. The devolved Welsh legislature intends to pass a law this year doing just that.

Not everyone is convinced this would increase donations. Among the sceptics is John Fabre of King's College, London. Spain has an opt-out system and leads the league with around 32 deceased donors per million; so does Greece, and it lurks near the bottom with four. Americans, like Britons, have an opt-in system, but also one of the highest donation rates in the world. Culture and capacity may matter more than legal regimes. Spain succeeds by managing the medical requirements of organ donation superbly and selling it emotionally to the public.

A task force which examined the matter in Britain in 2008 concluded that the number of deceased organ donors could be increased 50% by 2013 mainly through better donor identification and referral and more efficient organ retrieval, and that these should be tried first. Things have improved. There should be about 34% more donors in the 12 months to the end of March than four years ago.