I have owned a D3 and D4(current car) and my parents have owned many offroad vehicles, currently they are in a Prado 150. I have driven their 150 quite a bit on trails, they have driven it around Australia several times.
The biggest thing that keeps breaking on the 150 is the front wheel bearings. The aussie dirt/dust/salt doesn't do them any good other wise they have had almost zero problems with it in the 200,000+km they have driven it. It is extremely tough, the diesel will last forever if serviced correctly and there is 100000000000 aftermarket options for everything. If some thing does break other companies make just as good or better than oem parts cheaper(terrain tamer ect).
My D3 was a 2005 from Chicago, IL(I'm an aussie living in the US) so it had rust and corrosion issues from the winter salted roads but it had the rear locking diff options and was stupid cheap. It had 90,000 miles on it when I bought it and almost 140 when it was rear ended and written off. LOTS of stuff broke, never leaving me stranded, but just lots of little random annoying little stuff. I absolutely hate the V8 that's in it, I wish the US wasn't so anti diesel, which you wont have that problem being in Scotland. Even in base spec the D3 smashes the 130/150 top spec out of the water in luxury items, its bigger and more comfortable, quieter, better handling on road. For the D3 if you offroad it expect to change the lower control arm bushes every 30-50k miles. Between 90-130k miles expect to replace most of the air suspension system, another bonus for you living in Soctland you can get the D3 with coils, which is the absolute base spec but still a great vehicle. The base model SE diesel with coil suspension I would say is slightly better than the Prado, as most of the electroic things to break have been removed.
My new D4 is 2012 and just about to hit 100,000miles. In the 10,000 miles I have had it, it hasn't had a single problem. It's quite a bit more lux than the D3 but just as good or even better on/offroad. The Land Rover traction control is just incredible.
Comparing the Discovery and the Prado offroad. Straight out the factory I would say they are very similar in capabilities. The disco is more comfortable. The Prado will take more of a beating and keep going. I love my Land Rover but understand it's problems, I love working on cars so much so that I own 2 types of well made British engineering a Land Rover and a Lotus haha.
The Prado will be way cheaper in every aspect, just as capable and will have a much better resale if looked after. I would have bought one here, in the US, if they didn't come as the overpriced Lexus here.
