I used to drive a Minibus for work. I drove on a D1 (101) licence for 4.5 year until I left.
The job involved transporting workers from office to railway station and back. It also included transporting them from office to town centre at lunchtime and office to off site parking.
The structure was as follows. Company A hired the minibuses and provided company insurance cover for them. Company B was subcontracted to run the building facilities. Company C was the security company I worked for and were on contract to company B. The majority of passengers transported were company A employees. But some were from company B or C or even other subcontractors (catering, cleaners). Drivers were paid a salary, it was there main job and ran to a timetable.
Now I had problems with company C not having a clue about vehicles. I asked Company A why there wasn’t regular licence checks. A Company A employee decided to check again (I’d hadn’t been checked for over 2 years) and it was pointed out by me that 2 out of 4 drivers were unlicenced. They had passed their tests after 1997 and only had B licences. Despite that employees of company B & C still tried to send them out that lunchtime and I advised both not to as they weren’t insured. One had been doing the job for 2 years the other 8 months. They were later that day removed from driving duties and put on other work. Temporarily, the got some 8 seater people carriers on rental, enabling them to continue working. They were both retrained and sat D1 tests and passed. Company C picking up the tab.
Company A checked with their insurers about the D1(101) position for me and another driver. They also checked with the DVLA and VOSA. I checked with my union who couldn’t come up with a definite answer. I checked with VOSA and they wasn’t bothered as it was “staff transport”.
Both the DVLA and VOSA offer their interpretation, but also use the disclaimer that it does not constitute legal advice and to seek from a solicitor if you want a legal opinion.
So I never did manage to lean on my employers for a free licence upgrade 
Any payment direct or indirect that gives a passenger a right to be carried constitutes hire or reward.
If you have a hotel and offer a free courtesy bus to the airport: This constitutes hire or reward. Payment comes via money charged by the hotel for the room and is used to finance the bus. Even if the guest doesn’t use it, it still is hire or reward as the guest has the right to be carried.
If you have a nursery and offer a free minibus for the kids: This is hire and reward. Payment is indirect and passengers have right to be carried.
If you have an old folks home. Hire or reward. Same as above.
As you can see from the above, the passengers don’t have to make a direct payment for it to be classed as hire or reward.
If you have 16 mates on a jolly to Blackpool and you split the cost of rental / fuel equally and there is no element of profit, then that’s a NOT hire or reward. There are payments, but there is no profit (reward), no right to be carried and a private arrangement.
The trouble was, I couldn’t find a test case that set a precedent. There was some Magistrates Court decision about employee transport being hire or reward (something to do with Manchester Airport). But as this decision isnt’ binding and people call it a “grey area”.
I got no interest out of VOSA. They just couldn’t be arsed.
But if I had an accident with a load of fatalities, I’d be hauled over hot coals and in the clink.
Get independent legal advice.
My opinion is that it’s deemed to be hire or reward as you are being paid and the passengers have a right to be carried (i.e. it’s more than just a favour).
The only exceptions would probably come under Section 19 permits.