You won't. Trade agreements are hard and your politicians are scared wimps petrified of making a move lest because should they do so, the others will just tear them apart.
You've got CETA just about in the can. Would be good to move on that, but even then it would probably take a year. Everything else will take forever, if for no other reason than other countries know you are ****ed, and will therefore time is on their side in negotiations.
Add to that an 18% reduction in the number of Whitehall Civil Servants since 2010, and the massive workload about to land on their desks, and I can see every reason why Article 50 won't be activated for months.