If second preferences count «from the bottom up», there would likely be at least 500 seats won by Con or Lab before 2nd
pref votes by / for Dem have any relevance whatsoever (based on the 2010 election results).
Before you say otherwise, the UKIP and BNP have about 2 million combined nationwide
votes compared to roughly 200,000 for the Greens so it will be the UKIP / BNP second
prefs that are needed more.