Jihadist groups Isis and al-Qaeda are being funded by more than 250 Spanish businesses.
The businesses are mainly made up of telephone shops, butchers and grocery stores and the majority of the donations have been sent to Syria.
The small businesses are able to transfer the money without any controls by using the Muslim Hawala money-transfer banking system.
“The network has expanded recently and now includes some 250 Hawala companies in Spain.”
Hawala is used by 150,000 Muslims in Spain to transfer their savings abroad. It is not controlled as it is outside the established banking system.
The secret network is mostly made up of Pakistanis in cities including Barcelona, Valencia and Almeria.
The hawala banking network in Spain has previously been used to finance attacks around the world.
Khalid Sheikh Mohammed, the brains behind 9-11, employed several Hawala agents in Logrono and Barcelona prior to the 2001 attacks.