A frugal life is an easy life!

A few years ago, before we were pushed into doing everything "online" I always taxed cars at the post office. I would tax cars for family, friends, etc.
In the past few years in computer land, I have been taxing my car only, using the online system using the code provided by the DVLA.

Today, I attempted to tax sprog1's car, that has been sat on our drive for months as he is now a student and it is just sat there, a waste.

First call was the post office, who informed me that all would be fine, providing I had log book, valid MOT and my own insurance certificate.
Once there, I was flatly refused a tax disc, on the grounds that my insurance does not have the car's registration plate assigned to my insurance!
The lady at the post office admitted that, I can get in the car and drive it legally, but I cannot pay for a tax disc on it.
I then rang the DVLA, I got a lady on the phone who was obnoxious and impatient.
I cannot tax the vehicle as I don't have insurance on the vehicle was the official line - I clearly do have insurance to drive the car, as my insurance allows me to drive any vehicle up to 7.5 tonnes in the UK.
Then you can tax it I was told - the post office will not let me as the vehicle reg is not on my insurance certificate - this is correct I was told, so which one is it?

Then a statement from this lady that was truly bizarre:
If the post office allowed you to tax the vehicle, without having the car's registration  number assigned to your insurance certificate, it would appear that you are driving the car legally when you might not have any insurance and could be driving illegally!

As I pointed out to the DVLA, car insurance is insurance on the individual, not the vehicle - she agreed
I pointed out that I was insured to drive any vehicle on my insurance - she agreed
I pointed out that I could legally get in this car and drive it - she agreed
If I do not have insurance on any vehicle, I cannot tell the police that I am ok to drive it because the post office allowed me to tax the vehicle without an insurance policy on the car - she agreed

This car tax fiasco got worse, I was then asked if my car insurance was a "motor trader's insurance policy?" - it is not - then you have no option but to speak to your insurance company and have the registration of the vehicle added to your insurance documents.
Firstly, this discriminates against me, why can a motor trader tax a vehicle without the registration plate being assigned to their insurance and I cannot?
Secondly, no car insurance company will allow me to add a second car registration to my insurance, free of charge, plus the government gets insurance tax from any extra payments needed. The DVLA work for the government, so it is in the government's interest to make people pay more, which in turn pays the government more money in tax... the lady from the DVLA did not have an answer!

I finally got home, now with a headache and contacted my insurance company.
After going through this joke with them, they inform me that I cannot add the sprog's car on to my insurance details unless I am the registered owner of the vehicle!
I again told them I only require an insurance certificate, so that I can put a tax disc on the vehicle. They eventually conceded and agreed to insure the car and place the vehicle registration on my insurance, for their minimum of one month - which would cost me £46! (This includes insurance tax to the government!)

So to tax a car for £125, under the government's and DVLA's system, will cost me £171, which includes extra insurance and tax on this insurance, which must be done again in 12 months time, it will take more than a week as I have to wait for a new insurance certificate to be sent out.

This current system discriminates against myself, as those in the motor trade do not have this applied to them.
This system costs more to the individual who abides by the legal process.
This system takes more than a week to do something that used to take about 10 minutes at their local post office.

What is the point?