It seems highly unlikely that Halfords would know anything.
I know why you are asking - a mischievous reviewer has said it is possible on the Halfords Website without explaining how - I'm going to fiddle with all the buttons again to see if I can work out if it is possible.
The 2017 Suntour HESC brochure (attached) makes no mention of MPH, only KMH. (This has the "new" style display - confirming that the one without animals is the 2017 model).
Interestingly there is a new version of the 250w HESC motor for 2017 with a through axle - this motor has peak torque up from 50NM to 60NM - I guess we won't be seeing that on a Crossfire-e soon.