MOT

I called the MOT people to find out why I hadn't had my first MOT letter advising me it was due. They informed me it was due but never offered a reason for non delivery of notification.
I gave my reg number and she told me I was being charged as a truck, and the fee was £77 or so. This is because its classed as a Private HGV on the V5.
I paid the girl and got a date one week later.
Turned up for the test only to be handed a receipt for £45.50, it was tested in the lorry lane but classed as a private car.
So although it's a HGV it's also a private car.
She passed, piece of piss, but I'm scarred for life, having a vehicle that's neither here nor there.
£45.50 thats a few pints of stout ok.

Please correct me if I have misunderstood your situation.
You booked a mot test for your wagon, which was directed to a HGV test lane, which I am assuming is because the wagon weights a good bit more than 3500kg, ( commercial vehicles are N classified) at a cost of £77.
However at the test centre because your wagon is registered as a private vehicle, M1 class, you are charged a private car rate of £45 ish.
It is a bit confusing but I think that you're charge the right fee.
However during your booking process, the telephone operator was only looking at your wagon weight, not its vehicle classification hence, why your were directed to Heavy Goods Vehicle test rates, not private vehicle test rates.
Malcolm

My MoT, NI, was always carried out in the "lorry" lane, except on one occasion.

It's a compact two berth coachbuilt which, I suspect, weighs less than some large cars.

The printed advice I'm sent directs me to a car type lane but the tester will wag me over to the lorry lane.

The lifts in the car lanes go to about 3,500 kg. and there's often a bit of an overhang out back.

Similar. They told me to go to the lorry lane. The test itself was very lax, and it worked out at £30.50 same as a motor. I never knew about not being able to actually book online, they sent me a notification after I phoned in. We had the wife's car in on Wednesday, went into the office and they gave me a Friday, two days away! Next time I'll just go to the centre and do it there and then.

£30.50... tis €93.46 here, the camper is tested as a LGV if under 3500 (I think) and some centers can’t actually take over 3500!

Motor Caravans as a Class 4 MOT, same as Cars.
However, if the Motor Caravan is too big/heavy to be tested on a car test lane it's done on an HGV lane but at the Class 4 price.

https://www.gov.uk/getting-an-mot/mot-test-fees

Glad to hear it hasn't went to £77 or even £45.50

Years ago I was given the tip to book the van for an evening appointment as there are very few heavy or commercial vehicles, so the lane is free. I usually find the guys helpful and interested in the van which makes the process less stressful.

Davy