You can't.
Well, slight exaggeration. There are a couple of websites with results for very specific areas; David Boothroyd has published ward results for
Westminster and Paddington since 1900 and
Tower Hamlets 1964-1998, a former LibDem councillor in Sheffield has published results
going back a couple of decades. There's probably more out there that I don't know about. Also, there's some stuff on wikipedia; Manchester has especially good coverage (goes back to the mid 1970s, IIRC). Newcastle used to have an archive going back to 1982 on their website, but it was scrapped years ago.
