He said: "About half of their revenues, they receive between 2.5 million and 4.5 million dollars a day across all sources, but oil is very much the highest of that and most of that is sold in fact to the regime of Syrian president Bashar Assad.
"But we are making an impact, we're seeing taxes in Mosul and Raqqa forced to go up, we're seeing the salaries to the foreign fighters that go there go down, and we're also seeing the smuggling routes being closed off so we are defeating Daesh using financial means."
Pressed by MPs on what attempts are being made to cut off the terror group's main source of income the minister admitted that Isil does not keep or share accounts so it is hard to estimate exactly what it makes.
He added: "We are fully aware that their main source of income is the illegal sale of oil to the Assad regime. We've closed off other avenues but it's to the Assad regime."
The estimate follows news that British RAF fighter jets bombed the Isil-held Omar oil field in Syria over the weekend.
Brimstone missiles were used to destroy cranes which had been brought in to fix previous damage inflicted on the oil field by coalition bombing.
Source: http://telegraph.feedsportal.com/c/32726/f/579309/s/4ccfdf55/sc/11/l/0L0Stelegraph0O0Cnews0Cworldnews0Cmiddleeast0Csyria0C120A9610A90CIsil0Eterrorists0Eraise0Eup0Eto0E3million0Ea0Eday0Eto0Efund0Eground0Eoperations0Bhtml/story01.htm