Weight/Noseweight

3.55kg is not much. You probably could not find a nose weight scale with that degree of accuracy. The final nose weight will depend on how you load the caravan. Don't put heavy items right at the back and be careful  not to exceed the MTPLM. I guess as you are an HGV driver you'll have access to a weighbridge. You'll be surprised how easy it is to overload the van.

Towing Weights (as per hand book) - With brakes on gradients up to 8% - 2000 kg, With brakes on gradients up to 12% - 1900 kg.

So for caravan to car ratio would I go off the 8 or 12% gradient?

In my view neither. 8% is considered suitable for wheelchair access ramps etc and so not that steep. The 12% (for start on grade) is used by manufacturers to give the maximum tow load. Useful for comparison in my view but not really a useful guidance on UK highways as 12% is only 1 in 8.3 grade. I want to know that I can start on a 1 in 5 and preferably steeper. I don't think you will have a problem with hill restarts though up to 1 in 5

I would have prefered more hitch capacity though and probably around 95kg but it is what it is. The general guidance is between 5% and 7% and I aim for around 5.5% personally 

As you are buying a new van, I would ask the dealer to have the van, as purchased, weighed and a record of the actual weight provided, vans can often weigh more than the stated MIRO, and this will eat into your payload.

Then weigh everything you put in the van, keep below your plated MTPLM, and then take the fully loaded van to be weighed again.  This is the only way to be sure you are not overweight.

You  could ask if a weight upgrade is possible, but this   would likely leave the van weighing more than the kerb weight of the car, which is not good.

Personally, I would rather have the weight upgrade and change the car!

The payloads on U.K. vans are not generous these days.

What is your allowable gross train weight as stated by Audi?

The nose weight of the van as supplied will not necessarily conform to any % you have seen stated, it will be what it will be, and you will have to load it to achieve the 85kg your car can take.

Put stuff you will use in the van, in the van, all outside stuff and anything very heavy will have to go in the car.

Will you be fitting a mover?  That will eat into your weight allowance.

You  could ask if a weight upgrade is possible, but this   would likely leave the van weighing more than the kerb weight of the car, which is not good.

Not quite true Kj, a weight upgrade does not need to be fully utilised but still provides a margin of error. 

Yes, true, but I would say at least 95% of the time people do use pretty much all of their allowance, especially when allowances are small!

The proposed van is big, very wide, lots of storage, the temptation would be to fill it up, especially if there are children along too, the layout is 6 berth.

Looks like an upgrade to 1800 kg is available.

Change of car is not an option really. We have actually changed our minds about the 868 and are now looking at an 840 with a MIRO of 1545 kg and a MTPLM of 1724 kg, so slightly less than first stated but not by much. (although one option of this van comes in at MIRO 1600 kg and MTPLM 1779 kg, which almost pushes me towards the lighter version)

The van would come with a 2 wheel motor mover, I just realised the other day this would eat into the payload, I thought this would be accounted for in the MIRO as its supplied with the new van! Seen they can weigh up to 60 kg??

Kerb Weight (unladen weight) - 1800 kg, Gross Vehicle Weight - 2355 kg. I could not imagine having 555 kg of weight to add to the car but could possibly be around the 2000 kg which would help the weight ratio. There will just be me and the wife and a 1 year old using the van, mostly for long weekends throughout the year and the odd longer holiday each year. 

Was planning on taking the car to a weigh bridge tomorrow to get an exact figure of car kerb weight, see how accurate the handbook actually is!

Good idea to take the car to a weighbridge because what's in a handbook can be nothing more than a rough guide. After all, any published kerbweight figure cannot be specific to your car. Variances of up to 150kg are not unusual.

2 wheel mover would be just over 30kg, 4 wheel one will be 60+kg.

You will need a gas bottle, and a decent battery to operate the mover.

Hook up cable, water uptake/pump, winding handle, and anything else that comes with the van as supplied from the factory should be part of the MIRO.

So, took the car to weigh bridge yesterday - 1840 kg, car handbook said 1800 kg so not too far off, handbook account for driver at 75 kg, also in the car was my 1 year old in his car seat and base and a few other things that added up to a total of 30 kg, so Audi actually not far off with the handbook weight of 1800 kg. I have no doubt by adding the wife and some other essentials when going away the car weight would reach the 1900 kg. So instead of going off the handbook kerb weight I am more inclined to go off of 1900 kg when working out the car to caravan weight ratio as I would very rarely, if ever be towing with nothing in the car and just me.

Only thing to decide now is what van to pick, I am definitely decided on the Elddis 840 but the two I am looking at come in at different weights, one version is 55 kg more than the other giving it a total MTPLM of 1779 kg, if ever fully loaded would this be ok?? I think probably yes, towing at 93% ratio but confident with driving carefully and my experience of artics I would be OK.

Appreciate everyone's comments.