I'll suggest two, both of which are US based, but available through the internet.
"The New Wood Finishing Book" by Michael Dresdner from Taunton Press. It's more focused on finishing new wood rather than restoration, but it does a good overview of what to do, and why. And it's very readible and understandable.
Also from the US is "Great Wood Finishes" by Jeff Jewitt. I took a course from Jeff a few years ago, and aside from his experience as a finisher, he explained the why (artistically and chemically) of different finishes.
I'm sure there are some very good books written by UK authors, and if you're more interested in restoration, you're likely to get more information from this side of the pond than the US.