RACHEL SAVAGE THE head of one of Tanzania's biggest firms, Mohammed Dewji, said he plans to float an agriculture company worth up to $4 billion in New York or London next year, with money raised mainly from development banks. Russia's invasion of Ukraine in February sent global grain and fertiliser prices soaring, though they have retreated in recent weeks. Inflation has subsequently risen in many African countries. Dewji, 47, whose family conglomerate MeTL Group employs tens of thousands, said the new company will produce grains and edible oils in Tanzania, Mozambique, Zambia and the Central African Republic. "This is a…