The mysterious shrinking Lib Dems

Voting shares, election day 2010:

Conservatives         -        36%  
Labour                     -        29%  
Lib Dems                -        23 %

Average of last 5 YouGov daily tracking polls:

Conservatives         -        41% (+5)
Labour                     -        35% (+6)
Lib Dems                -        16 % (-7)