I've heard theorising that the "floor" for a major party is about 20% - that this is the percentage of the population whose vote isn't swayed by facts or events, and who would continue to be loyal if the sun went black.
If this is true, then the drop from 45% to 25% polling for the Tories represents a loss of eight out of ten of their non-hardliner voters. This means that while there isn't much further that they can fall, it also means that the party will now be driven by the need to posture to those hardliners, whose priorities may not be the same as those of the rest of the country.