LONDON — Britain’s first biofueled passenger train pulled out of a London station on Thursday at the start of a six-month test intended to measure the feasibility of replacing diesel power with biofuel. The train, run by Virgin Trains, will use a blended fuel made up of 20 percent biodiesel, which is derived from biological material - typically vegetable oil. Several British train companies are weighing whether to use biodiesel in their locomotives, and the test is being run in collaboration with the Association of Train Operating Companies, which represents Britain’s train industry, and the Rail Safety & Standards Board. The train will run for six months, during which time engineers will measure the fuel’s effects on the engine. If the experiment is successful, Virgin hopes to switch all its diesel-powered trains - which account for 78 of its 131-train strong fleet - over to biodiesel. Virgin Trains says the move could cut emissions from the trains by 14 percent. Virgin eventually wants its diesel-powered trains to run exclusively on biodiesel, which would require modifications to the train’s engines.