I'm no master of UK politics, but it seems like the Lib Dems have had quite a run in the local by-elections, without any noticeable uptick in nationwide polling. Any theories as to why this could be? Is this a common occurrence?
Yes very common. The Lib Dems usually do far better in local elections than they do in national elections and especially in local by-elections. They were doing very well in local by-elections prior to the 2017 GE but then they lost seats in the local elections and their national vote share fell even further at the GE. The Lib Dems have always been a more 'localist' party than either the Tories or Labour (who are very much 'national' parties) and thus most of their wins in these local by-elections are fought over local issues such as potholes, rubbish collection, trees etc. or the general competence (or lack thereof) of the Tory/Labour run council. These wins have nothing to do with national politics and unfortunately for them people don't choose the government based on 'who'd be most likely to fix the pothole outside my house'.
