Thanks to everyone who took the time to reply. For some reason I haven't received any notifications for the past few days so have only just seen the last few replies.
Having spent a lot of time researching the local market, we've ended up changing tack and putting down a deposit on a 2-litre diesel Kia Sportage with automatic transmission. While in theory a petrol engine might have suited our overall needs better, the choice of suitable petrol vehicles is just so much more restricted – and, of course, diesels tend to deliver more pulling power at lower revs, making them typically better suited to towing.
So in the end we decided it makes more sense to go for a diesel and amend our driving habits and balance the use of our two vehicles (my wife has a petrol-engined car) to make sure the diesel gets sufficient longer runs to hopefully avoid any DPF-related problems.
We'll be collecting the car sometime next week and in the meantime have found and bought the ideal caravan, which we're due to collect in about three weeks' time. It's all coming together