What kind of people usually vote for the Lib Dems in the UK ?
Varies widely depending on context. Their activist base has always had a lot of people who believed in liberalism as a political philosophy, but until recently this applied to very few of their voters and even now that's not the only major current.
Their historic strongholds were areas that didn't fit with the dominant political cultures of either the Tories or Labour (mostly relatively working-class rural areas, often non-English and non-Anglican.) To that they added in the period 1979-2015 voters who didn't like the dominant party in their areas, people impressed by pavement politics and a lot of cranks. In 2005 and 2010 they also won a lot of students and a lot people who viewed themselves as being too left-wing for Labour.
Most of these voters were repelled by the coalition government, and since 2015 their recovery has been concentrated in highly-educated middle-class areas, often wealthier than the norm, some of which they hadn't previously been strong in. However, in local elections their support is more likely to reflect older patterns of support (and a lot of their local voters don't vote for them nationally) and they are also able to have huge spikes of support in by-elections because they can play the role of a catch-all "down with this sort of thing" party.
