HEY BRITAIN. Vote YES tomorrow!

So Britain votes on changing its voting system tomorrow.

via the UK Polling Report

ICM’s final call poll for the AV referendum is very similar to the ComRes poll yesterday. Topline figures are YES 32%, NO 68% – a landside victory for NO. 

ICM also included standing voting intention, with topline figures of CON 36%(+1), LAB 37%(nc), LDEM 15%(nc)

Which means that there are a lot of Labour voters either voting NO or sitting it out. Here's the thing - I know you all hate the Lib Dems now - but a YES vote is basically unambiguously bad for the Conservatives, which is why they are the ones leading the NO campaign. What is going on, why isn't this a shoe-in?