Complex sentence: The biggest geographic trading center is the United Kingdom, primarily London, which according to TheCityUK estimates increased its share of global turnover in traditional transactions from 34.6% in April 2007 to 36.7% in April 2010.
Split into simpler sentences: The biggest geographic trading center is the United Kingdom, primarily London. According to TheCityUK, it is estimated that London increased its share of global turnover in traditional transactions from 34.6% in April 2007 to 36.7% in April 2010.