I think it also goes back before they new oil was there. Britain at one time occupied Iraq in the days when "The sun never sets on the British Empire".
Here's an excerpt from a website the link to which is below:
"British Colonialism and Repression in Iraq
Britain set up a colonial regime in Iraq after a long military campaign during World War I. In response to Iraqi resistance, including a country-wide uprising in 1920, British forces battled for over a decade to pacify the country, using airplanes, armored cars, firebombs and mustard gas. Air attacks were used to shock and awe, to teach obedience and to force the collection of taxes. Winston Churchill, as responsible cabinet minister in the early years, saw Iraq as an experiment in high-technology colonial control. Though officials in London sometimes had qualms about the violence, colonial administrators on the ground like Gertrude Bell expressed enthusiasm for the power of the imperial military enterprise. "