How a General Election could look today.

2010 General Election votes by party across the UK
Conservatives 10,726,614 - 36.1%
Labour 8,609,527 - 29%
Liberal Democrats 6,836,824 - 23%
UKIP 919,546 - 3.1%
Green Party 285,616 - 1%

the rest 2,313,253 - 7.8%
turn out 29,691,380

http://cdn.yougov.com/cumulus_uploads/document/y4jsox8pu0/YG-Archive-Pol-Sun-results-050613.pdf

So according to YOUGOV

Conservatives keep 69% of their vote from 2010 and then lose 21% to UKIP 6% to Labour and 2% to the Lib Dems with 1% to the Greens

Labour Keeps 86% of their vote from 2010 and then lose 6% to UKIP 3% to the Tories 2% to the LibDems and 1% to SNP/PC & The Greens

Liberal Democrats Keep 36% of their vote from 2010 and then lose 30% to Labour 12% to the Tories 12% to UKIP & 7% to the Green Party 1% to SNP/PC

Now the bit I have to be liberal with is that their is not as of yet a figure for people who voted UKIP & Green in 2010 and how they intend to do so now. (ie if they now vote lab/con/ld etc) Also in to the mix is the half million BNP voters. As much as UKIP have done their best to keep them out. It can not be any stretch of the imagination feasible that a anti european BNP supporter would find much difficulty voting for UKIP. Then again as with Greens and UKIP we don't know who they voted for before.

But with all that in mind the calculations are as follows.

Conservatives 10,726,614 keep 69% = 7,401,363 They gain 3% from Labour = 258,285 & gain 12% from Lib Dems = 820,418 new total votes =  8,480,066

Labour 8,609,527 keep 86% = 7,404,193 They gain 30% from Lib Dems = 2,051,047 & gain 6% from Tories = 643,596 new total votes = 10,098,836

Liberal Democrats 6,836,824 keep 36% = 2,461,256 gain 2% from Tories = 214,532 & 2% from Labour = 172,190 new total votes = 2,847,978

UKIP 919,546 gain 21% from the Tories = 2,252,559 gain 12% from Lib Dems = 820,418 & gain 6% from Labour = 516,571 new total votes = 4,509,094

You now have (ge2010 difference in brackets)

Labour 10,098,836 - 34.% (+5%)
Conservatives 8,480,066 - 28.5% (-7.6%)
UKIP 4,509,094 - 15.1% (+12%)
Liberal Democrats 2,847,978 - 9.6% (-13.4%)

the rest 3,755,406 - 12.6% (+4.8%) has grown due to the amount of don't knows and won't votes from all parties
Also assuming same turn out 29,691,380