The number of equines in the UK is now higher than in 1900; back then, most of those equines would have been working animals; now the vast majority are kept for leisure purposes.
However, with rising fuel costs and a growing desire for more sustainable ways of living, maybe the working equine is on its way back, at least on a small scale.
Guides & articles:
Horse Drawn Farm Machinery D.J. Smith
Starting to Drive Sallie Walrond
The New Horse-Powered Farm Stephen Leslie
The Working Horse Manual Diana Zeuner
Discovering Horse-drawn Vehicles D.J. Smith