London has made real progress in reducing new HIV diagnosis.

And that's because we know what works.

Be sure, know the four ways to prevent HIV.

One, test regularly and know your status.

Two, condoms can prevent HIV and other sexually transmitted infections.

Three, prep is a pill which can prevent HIV.

Four, undetectable.

Also known as U equals U.

Means people living with HIV on treatment cannot pass it on.

Be sure, know the four.

Visit doitlondon.org.

Hello and welcome to the Intelligence from the Economist.

In London, I'm Jason Palmer.

And in New York, I'm John Fassman.

Every weekday we provide a fresh perspective on the events,

shaping your world.

From building tactical bat houses to activism around one very old mulberry tree,

it's clear that Britain has chokingly restrictive planning laws.

We ask why cities can't grow outward or upward,

and how one tree can prevent hundreds of new homes.

And earlier this month, an advisory group warned diners

to avoid eating Atlantic lobster for fear that fishing lines

...