Money managers should be ready for “a lot of inefficiency” and currency fluctuations as Prime Minister Theresa May kicks off the official process of the U.K.’s exit from the European Union, a legal expert has told CNBC.

Sebastian Vos, co-chair of global public policy and government affairs team at legal firm Covington, warned currency traders that they should expect lot of uncertainty surrounding the negotiations in the coming months. Vos, a former member of the European Commission, added that sterling could gain or lose 50 percent of its value as the talks unfold.