Obsurd!
I would get someone in to give you a price to, dig a trench, make a concrete bed for the post and lay the EV Ultra cable, leaving Motability contractor to just install the charger.
Even ring an electrician for a price to fit a charger!
“additional work 20m trench, 15m extra cable & a post to house charger”
I’d query that as Motability allow up to 15m of cable for a standard install!
https://www.motability.co.uk/get-support/faqs/non-standard-installation/