Premier is quite correct, very different classes of insurance.
The main issue is that you as the CPO do not have any insurable interest in the clients vehicle. You simply can not insure the vehicle in your name as you have no financial interest in this car. It is the same as the fact I can insure my Wife's Life as I have a financial interest in her being there to look after my kids, I can insure a Business partner or fellow Director / Key Employee as they affect my business. But I can not insure there cars there is no financial interest.
Traders policies get Customers Vehicles covered, as the wording of these as a rule is "Vehicles in the Custody, Care or Control of the INSURED for Motor Trade Purposes" So a Traders policy would not cover for Hire or Reward, or Close Protection. Generally two Trades most motor trade insurers won't touch with a barge pole.
Even if it was possible, a number of Traders policies limit the Value or maximum indemnity so £20K would be nowhere close to your new clients S Class.
1. You should be added to the car insurance (at clients expense). You need to check this is done each year as if caught without insurance you get the points and yes it happens. A client of mine now has points as his Principal didn't renew the car insurance. NOT good for a chauffeur!
2. Or you buy your own car, get the RIGHT (Chauffeur / Hire Reward) badge and pay the insurance premium attached.
3. Don't confuse the insurance exposure of Driving and then CP work. In a simplistic form The Road Traffic Act covers the actions in the car. So the motor insurance is covering the CP aspect of the task whilst the client is in the car. Once you are out of the Car it's public liability or professional indemnity exposure as a CPO.
Premier is spot on Efficacy or Inefficacy (insurers can use the two phrases) it is vital for Security work.
Insurers historically exclude liability for the inability of the insured or it's products to do what they are intended to do. So if you have a crap builder build you an extension, it leaks, it won't pass building control, it's poorly built it falls down. The Public Liability cover will Not respond. Nothing is damaged, No one is hurt there is no claim. The issue is related to performance of the contract i.e to build a decent extensions and failure to fulfil is a standard exclusion.
As a result certain Trades in insurance have the wider cover to add back in Efficacy. Hence if your mechanic does a cam belt change wrong, if the engine goes he is insured.
It is the same for Security SOME polices add the cover back in so the failure of the Security Guard / DS / Event or CP Team to do the job correctly and someone getting injured or property being damaged as a result of the security "failing to fulfil" is covered. But a number of policies don't have this so you need to check.
On a practical note some High Net Worth motor cover is very strong and it will give your client Any Driver over 30 to include Staff. The policies are agreed value on most prestige cars (unusual) and the irony is the policyholder only can get comprehensive cover to drive any car not belonging to them which is VERY useful for them depending on the circles they move. I can help with these if you wan to introduce a client.
HTH
JC