There is a stereotype of bustling internet cafes in Lagos full of opportunist young men earnestly trying to dupe recipients of their messages into supplying their credit card details. Three thousand miles away, a very different breed of Nigerian scammer can be found in the cafes of Knightsbridge, central London, funded by the very tax dollars that are so badly needed to develop their homeland.

Between the two cafes is a web of corruption, in the middle of which are the Chibok schoolgirls, now entering their fourth year of captivity. Dismantling the web will be slow and there is more to be done, not only in Nigeria but also here in the UK, to make that happen.

Three years after the world reeled in shock as 276 female school pupils were kidnapped from their classroom, the media attention may have gone away, the celebrity outrage faded, but the vast majority of those girls still remain in the hands of Boko Haram. Fuelling the original attention was one fundamental question: how on earth can a militant extremist group kidnap hundreds of schoolgirls, and get away with it - for three years and counting?

Nigeria's battles with the scourge of corruption are no secret and its link to insecurity, and in particular the rise in extremism, is increasingly being understood. This is especially true of the defence sector. Defence corruption is more than just a waste of public money - it can actively enable the insurgent.

War on corruption

In Nigeria, corruption fuels Boko Haram's narrative that the state is corrupt, and that only with Islamic law can Nigeria provide a fair and just society. The conclusion is shaky, but the premise that state corruption in Nigeria is a problem isn't; more than $15bn of Nigerian procurement funds are missing at the hands of military officers. This is money that was needed to address Boko Haram 10 years ago, and that is still needed now to contain them. Training, intelligence, administration and communications have all been hindered, and in return Boko Haram has killed thousands of Nigerians and captured many more.

President Muhammadu Buhari was elected in 2015 on an anti-corruption platform, but his results have been mixed. His "war on corruption" borrowed its nomenclature from Bush's "war on terror" and Nixon's "war on drugs", and like its predecessors, results have reflected neither the vociferousness of its proponents nor the industriousness of its foot soldiers. Criticisms of his efforts have ranged from politically motivated prosecutions to ineffective reforms. The scale and depth of the problem makes setting priorities for reform difficult - last year, we published our recommendations for how to tackle the problem. And some positive change has happened, including the amendment of the Public Procurement Act so that defence is included alongside other sectors, instead of being treated as a secretive exception.

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At the 2016 Anti-Corruption summit in London, David Cameron whispered of Nigeria's status as a "fantastically corrupt" country. Buhari's response to the gaffe was accurate, if deflective: "I am not going to demand an apology," he said, "I am demanding a return of assets." He had a point.

Whether it's the five million Nigerians facing starvation, an elderly patient unable to gain the medical access they desperately need - or indeed a mother of a young girl who has been cruelly snatched from school by Boko Haram, corruption is not a victimless crime.

Corrupt officials cannot steal public money without a place to hide it. According to Transparency International research, at least £4.2bn of property in London is owned by individuals who are a high corruption risk, of which at least £77.5m comes from Nigerians.

General Sani Abacha reportedly moved millions through British bank accounts controlled by him and his family. The former national Security Adviser Sambo Dasuki has been accused of stealing millions with the intention of buying military equipment to fight Boko Haram; he allegedly spent it on properties in Dubai and London. More worryingly, James Ibori, a former Nigerian governor who is one of the only overseas officials to be found guilty in UK courts of money laundering, has now been released and is aggressively pursuing an appeal against his charges, employing top lawyers with the same money that it is claimed he stole.

Not a victimless crime

Last year the UK and Nigeria signed a memorandum of understanding on the recovery of corrupt money, but there is no public information to suggest that progress has been made since then. However, plans to introduce a public register of the real owners of overseas companies that own property in London will bring much-needed transparency that will make it harder for corrupt foreign officials to use London property to hide their dirty cash. Likewise, new powers that Transparency International has been campaigning for, Unexplained Wealth Orders (pdf), will provide law enforcement agencies with a sharp new tool to investigate suspicious assets.

UK companies can also be complicit in Nigerian corruption. An investigation by Global Witness has recently alleged that Shell paid $1.1bn to the former oil minister and convicted money launderer, Dan Etete, in order to gain access to one of Africa's biggest oilfields. That's more than the entire Nigerian health budget in 2016.

OPINION: Can Nigerian youth destroy Boko Haram's caliphate?

If Buhari remains healthy, there will be a champion of this crusade inside Nigeria, but global financial centres need to also ensure they are not acting as safety deposit boxes for those stealing from the Nigerian public purse. Whether it's the five million Nigerians facing starvation, an elderly patient unable to gain the medical access they desperately need - or indeed a mother of a young girl who has been cruelly snatched from school by Boko Haram, corruption is not a victimless crime.

Salaudeen Hashimu is a programme officer for the Civil Society Legislative Action Centre.

James Ancell is a project manager for Transparency International.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.