You should have had the option of 5m or 8m cable when completing the pre fitting online info. I was in the same boat as the position I picked looks like the 5m is going to be a stretch so I asked OHME what it would take to change and they said £200.
I think Ohme pick prices out of a hat n the day!
As a Motability user you have the opyion of 5 or 8m.