According to YOUGOV POLLING
21% of Conservative voters from the 2010 General Election
12% of the Liberal Democrat voters &
6% of the Labour vote
Is now voting or saying that they will vote for UKIP.
So at the 2010 General Election
Conservatives got 10,726,614 votes
Labour got 8,609,527 votes
Liberal Democrats got 6,836,824 votes
So using YOUGOV reasoning UKIP gets
2,252,559 votes from the Conservatives
820,418 votes from the Liberal Democrats
516,571 votes from Labour
totalling 3,589, 548 votes in total for people who previously voted for the main three.
If you add that to the 919,546 UKIP got in the 2010 General Election it makes 4,509,094