Western countries, led by the United States and European Union, imposed a range of sanctions on Russia in late March 2014 after the Kremlin invaded the Ukrainian peninsula of Crimea. The second wave of sanctions followed in late April of the same year, after Russia began its covert military intervention in the Donbas, fomenting a fake insurgency that has cost more than 10,300 lives so far. The third wave of sanctions started to be imposed in late July 2014 and in August 2014, after Malaysia Airlines Flight MH17 was shot down by a Buk anti-aircraft missile system that Russia had sent into Ukraine.

But almost four years later, Russia has still not responded to these sanctions by meeting its obligations under the Minsk peace accords, withdrawing its troops from Ukraine and ending its occupation of Crimea. The sanctions have hurt the Russian economy, certainly, but they have hurt the EU economy too. Does that mean that sanctions do not work?

No it does not. It means that these sanctions were ill-targeted, and not strong enough.

Proof of this came on April 9, when the results of the latest set of U.S. sanctions, announced on April 6, started to be felt in Russia. The ruble dropped in value (by 3 percent over two days) and about $16 billion was wiped off the net worth of some of Russia’s top oligarchs. Russia has in the past reacted to the imposition of sanctions by the West with sneering disdain, and imposed its own counter-sanctions, ostentatiously and absurdly depriving Muscovites of expensive imported cheese by crushing it under bulldozers, or steamrollering imported fruit and burning foreign bacon.

But the Kremlin’s reaction was muted and subdued to this latest round of U.S. sanctions, imposed because of Russia’s meddling in the 2016 U.S. presidential election. As this newspaper has long argued, to hurt the Putin regime, sanctions must target the only thing these gangsters care about – their vast, stolen fortunes. And that’s what these sanctions did.

Contrast, now, the Russian reaction to the United Kingdom’s decision to expel 23 Russian diplomats following the attempted assassination of former Russian spy Sergey Skripal in Salisbury on March 4. That measure was met by the Kremlin with sarcasm and derision: Russia expelled an equal number of U.K. diplomats, and shut down the British Council, a cultural organization. Arguably, the U.K. came off worse in the exchange.

It needn’t have. London is the city of choice for Russia’s corrupt elite to launder its dirty cash, and store value in the form of luxury real estate. U.K. offshore zones, lax company laws and weak banking regulations allow Russian oligarchs to construct webs of shell companies to conceal their ownership of valuable assets. London’s financial sector is thus a target-rich environment for smart, precision-guided sanctions that would inflict serious damage on Russia’s wealthy elite.

It’s time for the U.K. to follow the U.S. lead and start hitting Putin’s cronies where it hurts – their pockets. That means imposing well-targeted, powerful sanctions, propelled by a sufficient charge of political will.