The impact of incentives on European office rental values has resulted in significant changes in the ranking of the most expensive cities, according to international property adviser Savills. The firm compared 18 key city locations and found that when incentives are taken into account, London's West End remains the most expensive and Lisbon the cheapest. The study sees Paris CBD becoming the second most expensive, overtaking the City of London. Istanbul drops from sixth most expensive to 13th place, while Amsterdam slipped from eighth to 11th position.