The angle of rise and set of the sun at the latitude of South Wales varies by about 10 degrees all year i.e. 30-39 degrees for rise and set at the equator it's can be straight up -90 degrees .
I think it's the point where the sun rises and sets that is more important for you this is more problematical as it depends on the horizon .There are programs and formulae but as they don't know what the horizon is likely to be they will not not much help in prediciting . With a compass , clinometer and calculator you can work out the declination of a point on the horizon from an observers viewpoint and calculate whether or when the sun will rise or set at a particualr point on the horizon . You could also have a rough idea of the setting point before setting out and do a rough calc when you asses the horizon using the clinometer . You can also do a lot remotely if the information is accurate i.e observer and horizon heights ,distance between the two, azimuth and latitude is all you need . A specific case might be useful . Hope that helps or have I misunderstood ?