In reply to FesteringSore:
The budget hotels work in a similar way airlines or train travel. The prices start low (typically £29) then rise as they sell rooms. In popular locations, or if there is an event on locally on the date you want to stay the cheap rooms can sell months before the date.
Travelodge is generally fine if all you want is a basic room and bathroom, I've only paid more than the budget price, when they were the only hotel within 10 miles whee I needed to be. Premier Inn rooms are generally a bit nicer and the hotels often have more facilities, but tend to be slightly more expensive.
I've had some good deals with Holiday Inn Express, as low as £19. I've also turned up on spec following a change of plan and paid £100.
If you are looking for the 'hotel experience' rather than just somewhere to sleep, you need to look elsewhere.