It's always been like this - as has every other Honda Jazz I've driven. Seems to be a characteristic of the mk1 Jazz.

Like I say, great for nipping about locally with the CVT gearbox but I wouldn't want todo long journeys in it.

The problem is that an A5 is likely to have by default a firm ride, cost a LOT to buy and insure / run and if you want an auto, the VAG DSG isn't exactly one noted for long term reliability, especially if you are buying blind second hand (not knowing how it was used previously). Often cars get sold as such problems start to appear.

A lower spec car (including a good few from the VAG stable) with a longer wheelbase and more engine punch / better handling is likely what you need - reasonably priced, even now shod on sensible, common sized wheels and especially tyres (not expensive to replace), and if you can manage it, a manual gearbox.

My similar aged Mazda3 is fine on motorway duty (I did around 1000 miles driving down/back and in Cornwall for a recent holiday) and that only has a 1.6 N/A petrol engine with 105bhp.

I'd also make sure that you get a decent length test drive (over a wide variety of road types/speeds) of anything you look at (after getting the seat and steering wheel adjusted to your liking as much as you can) to give a representative experience.

To often, poor driving comfort only appears on longer, faster journeys, especially on fast-flowing winding roads. Similarly with cars shod on low profile tyres when only tested on smooth tarmac.

Wheelbase is the key to long distance comfort. In my humble.

That may be true in general terms, but a 2015 Honda Jazz (regardless of whether late 2nd gen or early 3rd) has a longer wheelbase than any rival other than the Renault Clio.

It also ignores the firmness of suspension itself. The OP mentions an Audi A5 he likes the look of, but going by the motoring press, Audi's were commonly derided for their ride being excessively firm (despite a lengthy wheelbase).

Before Brovid I used to drive to and from Milan four times a year to and from Cheshire. Nine hundred and something miles each way. Plus or minus 18 hours door to door including coffee/pee/lunch/fuel breaks as required.
Done it in all manner of vehicles from Mk1 Pandas, Escorts, Cortinas, Sierras,Merc 190s, Mondeos, Golf GTis, Volvo 850s, Volvo 940s, Rover 800s, BMW 3s and 5s even a Westfield a couple of times and latterly, Mercedes Es.

Without a shadow of doubt in my mind, the greater the distance between the front and back wheels, the waftier the ride.

I remember a Car magazine article on the then new Fiat 126 Bis (the water-cooled version). In it the great LJK Setright spoke of chap from Fiat UK who, when he had to drive to Turin, would always choose a 126. And they have a very short wheelbase!.

Indeed - the combination of the inate firmness (or not) of the suspension and the contribution to or against the ride quality from the size and type of wheel/tyre combo cannot be underestimated.

My parents' two otherwise very similar cars shows what a big difference just fitting smaller wheels and higher profile tyres make to ride comfort. Even with my car where the difference in the size when changing tyres and wheels was much less, the improvement in ride quality was noticeable.

One thing I've noticed via test driving cars or gleening from road tests/reviews on sites like this is how some car manufacturers either try to cover up poor chassis and suspension design that would ordinarily mean the car handles poorly by significantly firming up the suspension and fitting wider, lower profile tyres, often to cars that don't have the performance to warrant them.

Unfortunately some cars' firm ride doesn't reveal itself until the new car has got a year or two 10-20K miles under its belt. When I test drove a similar Jazz before I decided on my Mazda3 back in late 2005, I thought that the Jazz's ride was firmer, but not so bad. Maybe my test drive route didn't go on enough poorly surfaced roads and I was lucky.

Maybe the OP might want to consider tarding in the mk1 Jazz for a (supposedly) better riding mk2? Still as practical, though no torque converter auto (presume just the CVT or the hated i-Shift).

As well as the Jazz I have an automatic Skoda Octavia petrol estate for longer trips which is a great car, but like the Jazz is just a bit well, boring.

I have a budget of £18k ish but cannot decide what I want. Realistically, I need to be able to take 4 adults, plus stuff, over longer distances with ease and in comfort. As advised here, petrol is the way to go and it must be an automatic.

I'd quite like another SUV especially for the higher ride height and driving position but having had a couple of old petrol Qashqais which I found really underpowered I'm not sure.

I'm drawn to the crop of fastbacks as I like the way they look and seem to fulfil my brief. I'm concerned about running a petrol BMW 3 series GTbut like the VW Arteon as mechanically it would be similar to my current Skoda.