realistically 7 seats would not be used all the time but probably would 30% of all use.

That is only part of the question though, the other is whether the third row would be required to fit adults. Also, would the use of all seven seats be whilst travelling in Europe (or indeed going on hols anywhere)?. If so, you are going to need something bigger (or a large roof box, or a tailer) because a Zafira Tourer with all seven seats in use has 152 litres of boot space!. Other similar 7 seaters may have a little more, but to get more than about 200 litres you'd need to go up a step in size.

Re whether a Zafira Tourer 1.8 would manage 20k miles per year?, no reason why not if it is in good fettle and continues to be looked after. But the youngest 1.8 is going to be a 2015 car, so finding a good example may not be easy.

But for doing that many miles, I'd be thinking diesel. Know there is some risk re DPF's and how previous owners have used the car, but even so!

The Vauxhall Zafira initially came to mind, but then you mentioned you were willing to spend up to £18k. The Zafira is available for a lots less and categorised as an MPV rather than an SUV.

My father owned a 2006 Zafira 1.6. Generally happy. It was easy to drive and handled family day trips well. However, like most 7-seaters, the two rear seats can feel a bit claustrophobic, especially since the windows don’t roll down. They're acceptable for adults but more suitable for children. I was impressed that the Zafira's1.6 petrol engine could handle the whole family on board.

Another option to consider is the Toyota Verso, which I test drove a few years ago. It’s a decent car, but not particularly thrilling to drive, especially on winding country roads.

If you can find a good one, I recommend the Mazda 5. While I haven't owned it, I've test driven had a Mazda 6 for while, so familiar with Mazda engine and dynamic, so there might be some similarities. The Mazda 5 has sliding doors and, in my opinion, will likely offer a better driving experience than the Toyota Verso or the Zafira.

I also looked into the Toyota Estima. Many are imported, and they receive good reviews on this forum. However, servicing and parts availability could be something to keep in mind.