Depends on how you define "good". There's a difference between waterproof at zero pressure (like walking through mist) and waterproof at high pressure (like a downpour). The former type can be worn all day while the latter will make you sweat to the point where you'd most likely be less wet if you just took it off.
All manufacturers claim that their membranes solve this problem, but I've yet to find even one that works better than regular oilcloth - which is to say, works at all.
Now I'm not familiar with Scotland, but if it's anything like Ireland, where rain is mostly a light, constant drizzle, a waxed leather or wool jacket would be best and something two-layered like a M65 would work fine as well. In fact, I've worn a regular, untreated M65 in the irish mountains for a few weeks some time ago, and while the outer cotton layer was constantly wet, the water never got through the polyester padding.
On the other hand, if it's like central germany, with sudden, harsh downpours, a fibre-reinforced plastic poncho would be the best option, as jackets that stand up to such rain are uncomfortable and make you sweat. Just throw it on when it starts raining and keep it on your pack or belt otherwise.