There is a YouGov poll reported in The Sunday Times today which has the Tory lead over Labour narrowed to 2 points. The percentages are: Con 37%, Lab 35%, LD 17%.
Here, according to UK Polling Report's Swing Calculator is what would happen if there was a uniform swing of this nature across the country at the election:
Now I know that this does not take into account the story in the marginals which could tell quite a different tale but even so according to this Labour would be 54 seats ahead of the Conservatives. It is unlikely that the Conservatives could go against the national trend strongly enough in the marginals to be able to form a majority government.
It is now looking possible that it could be Labour with the most seats. If that was to happen it would be a catastrophe for the Conservatives.
I agree with James Forsyth in the Speccie that David Cameron needs to pull off a very strong speech at his party's Spring Conference today.