You will need to register the vehicle to pay VAT
Log in to use the Notification of Vehicle Arrivals (NOVA) service - GOV.UK.
You will need the original registration documents and the CoC (Certificate of Conformity)
The vehicle will be built for Right hand traffic so the headlamps will need changing and the speedo probably won’t read in mph anywhere so both the items will need reciftying.
Headlamps will be expensive but an easy fix.
The speedo will probably have an ecu involved so check with the manufacturer as to the cost
(Both of these items on a new MB will cost about €200 if specified by the euro customer, but £2,000 to put right over here)
You will then need an IVA to agree the headlamps/speedo are sorted, beware an over enthusiastic tester who will try and fail it if it has non factory standard bits fitted, if there are some and you dont want to remove them add them to the IVA application, but you will need supporying docs to prove they are type approved.
Once you have done all that, fill out a blank V5 application and send with the NOVA confirmation, foreign reg doc, IVA, CoC and some ID (utility bill of the company/individual to whom it will be registered) cheque for the tax plus £55 first reg fee and wait at least 10 days with bated breath.
Good luck!