The problem is paperwork, to sign the installation certificate the person must do the work or at least be in charge. There are three signature installation certificates, design, installation and inspection and testing but don't think these are used with scheme providers so once you select a firm that firm needs to do all the work.
There is no problem with work taking 4 or more years, it is the date it was designed that matters, so if I had started work in 2003 then it would need to comply with BS7671:2001 not BS7671:2008 or BS7671:2018 but you would of course need to paperwork to show design date.
But although the IET/BSi regulations allow that, not sure about scheme providers, so you may need to use the LABC route.
As it stands we are in flux with debates on how to handle TN-C-S earthing systems with EV charging, what it means is not important to you, but if in the future we use a different way around the problem needing say 5 core instead of 3 core cable that could mess it up, already we have seen changes, early systems needed earth rods, there are some now which don't need them, and early systems were not linked to DNO so they can remotely turn off car charging if there is a supply problem.
I am sure in this house I could lay cables for a charging point at bottom of garden without a problem. For caravans think we need 2.7 meters from a building, if any rule like that is made for EV then clearly you could have problems complying with some houses.
So yes you can fit the cable now, but that means selecting what type of charger now and where it will go, and agreeing to use same electrician to complete the work. So clearly not a sole trader.