Buses and Coach Transport in Spain
Buses in Spain are comfortable and efficient.
Although described as 'buse services', the vehicles
plying the routes are usually an air-conditioned coaches.
To the tourist the Spanish bus system may seem a bit complex
especially as there are many lines
covering long distance journeys. However buses are recommended
for both their comfort, price and convenience
for short trips and for longer excursions.
If you know more or less the journey you want to make then and just want to buy your ticket try the ALSA webite seems to have it all.
If you want know how to go to Spain overland from UK then National Express has a service which links most of the main cities in UK to Spain.