They are a kind of non-party really.
Why? Because they hold the balance of power and can swing either way but will always be the minority party in government. So their election 'pledges' are meaningless as, once in government they will be neutered by the dominant party. And if they cannot hope to fulfill them their policies are also meaningless.
They used to have some pretty lofty ambitions about reforming the electoral system towards something more democratic but this seems to have drifted off the radar now they have some 'power' (albeit chimeric).
What's most annoying really is that so-called liberals who are meant to take a pretty egalitarian approach to things (rather than aligning themselves with the working class and the left, or the upper classes and the right) have facilitated the arrogant stubborn and mostly misguided policies of a bunch of overgrown public schoolboys.
And unfortunately these boys think they have the right to run a country based on no experience, no academic or pragmatic understanding of economics, no conception of what 'hard working families' - their buzz-phrase - actually are.
We have the Lib-Dems to thank for that. And no, they don't have any credibility any more.