The provisions of the Terrorism Act 2000 seem fairly black and white: it's an offence to supply money or property to terrorist organisations, directly or indirectly, and to fail to report belief or suspicion that this might be happening.
But as crises continue to deepen in Syria, Iraq and Afghanistan, matters are not always so simple for charities that work in those places. Despite their precautions, they face the possibility that their funds and resources will be diverted into the hands of terrorists.
"Fraud happens in our sector in the safest and most stable places, and we work in some very dangerous places where very bad things happen," says the chief executive of one large charity, a member of the international development body Bond.
"And if resources are taken by a terrorist group - whether through a front organisation deceptively accessing them or an armed group forcibly taking them - there's the potential for a criminal offence to have occurred."
This means that a charity that is the victim of fraud, or even violent attack, could find itself facing criminal charges. Although this has yet to happen, it remains a constant concern.
The Charity Commission reminded charities recently about their duty to report any knowledge or suspicion of terrorist financing. This move came after a small number of incidents in which, it said, charitable goods and funds had been lost to proscribed organisations overseas.
It said that in one case, discovered during its investigation and enforcement work, the National Terrorist Financial Investigations Unit had concluded that an offence had been committed but it was not in the public interest to prosecute.
Buthaynah Ahmed, head of media for the aid charity Hand in Hand in Syria, says some of the risk can be mitigated by having strong supply chains and trusted local staff. "Our supplies are handled by our staff, so they never leave our care, which minimises the risk of diversion," Ahmed says.
Despite its precautions, the charity feels under scrutiny by the authorities. "There's more suspicion than there is trust," says Ahmed. "One member of staff was questioned for four hours simply because she was returning from meetings in Turkey."
Charities have also been affected by the fears of banks about their own anti-terrorism liabilities. The unnamed chief executive says: "Even a lot of the bigger agencies have had transfers to high-risk regions blocked."
To meet such concerns, he says, charities have to demonstrate more complex risk assessments: "It's also about design and delivery of programmes - how can we make them as safe and effective as possible?"
Jonathan Burchfield, a partner at Stone King solicitors, agrees that the way to minimise damage to a charity is robust risk assessment and emergency planning.
"Having an experienced crisis team is crucial," says Burchfield. "And it's essential, if anything does go wrong, to make a serious incident report to the Charity Commission so it can help.
"I have huge respect for the trustees who make that call, and if you feel your beneficiaries need your help, it's a call you have to make."