There is still a lot of softwood firewood sold in the UK, most likely in nets sold in garage forecourts and whilst in recent years there has been a move towards hardwood, there may now be a move back to more softwood as prices for hardwood timber rise faster.
Firstly, its quite important to know the difference between the two types of wood. Hardwood fundamentally comes from trees that lose their leaves in the winter, so trees such as Oak, Ash, Beech etc. They are slow growing (80-100 yrs to maturity) and therefore provide a dense timber. In contrast softwood grows much faster maturing in 25-30 yrs and the timber is therefore less dense. Trees include Pine, Larch, Spruce and Douglas Fir etc.
So, how about their burning qualities? Lots of people say that you shouldn't use softwood either because it burns too fast, produces too much resin in the chimney or smokes too much.
Well, in summary softwood is great for burning, but as with all wood fuel it has to be dried properly to below 20% moisture content. Whilst it has the same calorific value as hardwood by weight, being less dense you need sometimes up to as much as twice as many logs for the same weight, or energy output. As regards resins, there seems to be conflicting advice on this, but it seems that as long as the wood is dry the resins can actually act as supercharged fuel, so better, not worse than thought! As for smoke, well just like any other wood, if its not dried properly it will smoke.
One of the biggest advantages of softwood, if drying it yourself, is that it dries very quickly and probably takes half the time to dry and its also great for kindling. Much of the kindling sold today is softwood for this reason and the other benefit is that it gets the stove up to temperature very quickly which helps stove performance, increases 'draw' and reduces smoke.