I am looking for a split-tailgate mid size car, AWD or 4WD. Needs four doors, diesel preferred but petrol OK. I had a 1998 Sport range rover which was perfect (perhaps a little bigger than I needed) but wanted something newer (no more than 5 years old) and cheaper to run and service. Needs to tow a standard trailer or surf boat.
SUVs with split tailgates are reasonably uncommon (in fact, vehicles with split tailgates are uncommon). They need more parts, more seals, more latches, more hinges, etc. Most rear hatches these days are the single-piece 'hatch' type that swings vertically up and away, like an awning.
A smaller SUV that does what you want, and will tow a moderate load is the Renault Koleos. It's a twin under the skin to the new Nissan X-Trail (but the X-Trail has a single-piece hatch). Renault and Nissan are joined at the hip, in a corporate sense. The company does good engines (diesel 2.0 and petrol 2.5 both available) and the vehicle will tow up to 2000kg with trailer brakes and 750kg without.
I agree with you that the horizontally split tailgate has some advantages: your gear doesn't fall out when you undo the hatch, and it's not a bad table to change the baby or eat lunch from, in the middle of nowhere.
(I've owned a RenaultSport Clio for over a year, and been very happy with it.)
If you decide you want the Koleos, give me a shout by e-mail - contact form here - and I'll put you in touch with a car broker who can secure the vehicle at a nice, low price, and insulate you from the typical dealer rip-offs as well.
I don't think the previous Koleos had a split tailgate, so you'll be looking at a new one, but the price is pretty sharp, and you could always ask the broker to secure a demonstrator, which would be cheaper again.
Full details on the Koleos: click here for Renault's official Koleos page.
Best of luck with it.