Obviously the more significant candidates there are, the lower the percentage vote needed to win a first past the post election. I seem to recall that there were results in Papua New Guinea where single member, first past the post seats were won with as little as about 5% of the vote.
In the UK there have been general election results, where the winning candidate had a lower percentage vote than in the Eastleigh by-election; but probably not in England. Belfast North in the 1979 general election, is the lowest I have found in a quick and superficial search (27.6% according to F.W.S. Craig).
Norwich South and it's not to find one in the Scottish results through the years.
Brighton Pavilion and Oldham East and Saddleworth in 2010 alone as well in England. And Argyll and Bute in Scotland in 2010 as well.
By my count, there have been 5 such results in England total (the 3 in 2010 and 2 in 1922, in Portsmouth Central and East Ham North). There have also been 7 such results scattered through the years in Scotland, 2 in Wales, and 3 in Northern Ireland.
