As there are already legal challenges to whether the PM can declare Article 50 without a new Act of Parliament [1] and that Parliament goes into Summer recess on July 21st until 5th September [2] then struggling to see how we're going to start much before end of September at the earliest.

[1] http://www.theguardian.com/politics/2016/jul/08/legal-attemp... [2] http://www.parliament.uk/about/faqs/house-of-commons-faqs/bu...