They have to wait for the ORR to approve the electrification for operation once they green light the use of it then electric trains can start to use it which is what I believe happens.
Is there not a problem introducing electric trains because the current diagrams interwork Man-Blackpool trains with other services, and they cant change the timetable because of the embargo after the timetabling fiasco earlier this year? So it will be May 2019 then....