Political turmoil caused by Britain's vote to leave the European Union could knock demand for air transport later this year, the director general of airport association ACI Europe said. Shares in major European airlines such as easyJet, British Airways owner IAG and Ryanair have been hard hit since the Brexit vote, due to fears over travel demand and whether flying rights will be affected. The vote is not expected to impact overall European air traffic levels this summer, ACI said in its monthly traffic update on Thursday. "However, the political instability and uncertainty it has created in the UK and beyond is already hurting business confidence and might end up doing the same for consumer confidence - this could affect demand for air transport later in the year," Olivier Jankovec said in a statement. Three percent of Britons with holidays booked this summer plan to cancel due to concerns over the value of the pound, according to results of a survey commissioned by online deals website Travelzoo and carried out after the Brexit vote. ACI Europe said May traffic data showed the impact of attacks and geopolitical tensions. Passenger numbers for Turkey were down 8.2 percent, while Russia saw a 6.5 percent drop. Overall, traffic at EU airports rose 5.5 percent in May, but dropped 2.5 percent for non-EU airports, ACI said. "Some of the leisure demand is shifting towards the EU market - contributing to boosting EU passenger traffic performance for airports in Portugal, Spain and Cyprus in particular," Jankovec said.