By David Milliken LONDON (Reuters) – Britain’s departure from the European Union has reduced the size of its economy by 6% so far – an annual cost of 140 billion pounds ($178 billion) – London mayor Sadiq Khan said on Thursday, with the shortfall seen reaching 10% by 2035. Khan, a member of the opposition Labour Party, which voted against Brexit in a 2016 referendum, based his statement on a report he commissioned from economic consultants Cambridge Econometrics, who estimated how fast the economy would have grown if Britain had voted to stay in the EU. “It’s now obvious that Brexit isn’t work…