How might the Lib Dem 8% break down ?
Assuming the Lib Dems don't contest in Northern Ireland or the speakers seat:
Reasonably the base Lib Dem vote is 2% - even in there worst 126 seats they should average 2% of the vote. At the other end the Lib Dems have 57 seats they hold, rounded to 63 for the maths and to reflect a few wild cards. In line with the Ashcroft polls I've gone for a 31% average in these seats - for some that might mean 20 -25%, almost certainly not enough to win to up to about 40% in other place pretty much a sure win.
To stand any chance of winning their held or target seats the Lib Dems will need to be polling abysmally in half the seats where they won't even keep their deposit.
But what of the seats the Lib Dems did well in last time but didn't win - thee seats where they polled above their 23% average? Things don't look good - in most of these seats the Lib Dems will do well to poll 5% and save their deposit. In the old days the Liberal party was famous for losing deposits but that was when you needed 12.5% to save it.
1% across 631 seats =1% national vote
126 seats where they get 2% adds 0.2%
126 seats where Lib Dems get 3% adds 0.4%
126 seats where Lib Dems get 4% - adds 0.6%
63 seats where Lib Dems get 5% - adds 0.4%
63 seats where Lib Dems get 7% adds 0.6%
63 seats where Lib Dems get 21% adds 2%
63 seats where Lib Dems get 31% adds 3%
Total Lib Dem vote nationwide 8.2%