[tlitody]

Look at any web site selling nice colour landscapes and see the prices they charge. Maybe 20 or 30 pounds rising up for bigger or canvas prints.
But mostly 20 or 30 pounds. So if you want £30000 salary a year you have to sell 1000 prints a year. But that is before costs which are considerable because you are going to have pay petrol and vehicle running costs. Camera equipment and printing costs and packing costs and shipping costs although packing and shipping can be passed onto buyers. And all of that is before tax.
So in reality you'll need to sell maybe 1500 prints a year at £30 each. But then you'll need a top quality website with online selling which has excellent search engine optimisation or you'll sell nothing via the web.
All the top UK photographers who are successful at this are all doing other things as well, such as running photography courses or commercial work for magazines or the likes of the national trust or english heritage. There are probably no photographers in the UK who make a decent living out of purely selling prints. And you will need to market your work very agressively. And your work must be the absolute best. Superb quality of stunning views that people actually want to buy. When you get a name for yourself and people buy your work just for your name then you've made it. Upto that point you will be just one of thousands who like the idea but never actually make it.
Ultimately it comes down to your ability and vision and above all your self determination to get there. It can be done but don't be surprised if it doesn't.

n.b 1500 prints a year is 30 a week. How many landscape prints have you ever sold? You'll need them on sale in many outlets to reach that number and you'll get only a fraction of the selling price if someone else is selling them for you. So you'll have to double the number of prints you sell and you'll have to actually produce them. That's 60 prints a week you need to make and package them. Hope you have time to do some photography.

Oh and just in case you think that you can sell them for more money, lets says 6 times more at £180 each, then just consider how many people will actually buy an £180 photographic print. Whats the most you have ever paid for a landscape print if you have ever actually bought one, and you are into landscapes. Yes?