Conservative lead up to seven points in latest YouGov poll.
Latest figures would leave the Tories 17 seats short of a majority.
Two Sunday newspaper polls put the Conservatives on 37 per cent.
But YouGov figures would still leave Labour as the single largest party.
Two per cent lead is the party's joint lowest since December 2008.
Conservatives remain just four points ahead of Labour in latest YouGov poll
With weeks to go before the election, polls still show hung parliament is likely.
Tory lead rises three points in wake of British Airways strike.
Latest YouGov poll suggests Labour would remain the single largest party.
New YouGov poll suggests the Conservatives' lead over Labour remains fragile.
Latest figures would leave Labour 33 seats short of a majority.
Tory lead rises to nine points in latest ICM poll and eleven points in Opinium survey.
Poll suggests an increasing number of voters would like to see a hung parliament.
Latest YouGov poll would leave Brown 19 seats short of a majority.
David Cameron and his party look short of the seats they need for a majority.
Latest daily YouGov poll suggests Labour could emerge as the single largest party.
New poll suggests David Cameron will struggle to win an overall majority.
Party reaches crucial figure of 40 per cent for first time since mid-February.
Voters also expect David Cameron to perform best in the leaders' debates.
Latest figures would leave Labour as the largest single party.
Tory lead recovers but hung parliament is still likely.
Tory lead cut to just two points in new YouGov poll.
Latest Ipsos MORI poll puts Tory lead at lowest level since December 2008.
YouGov poll for the Sunday Times (21 February) reveals narrowest Tory lead since 2008.
Conservatives on track for a small majority as party rises two points.
Tory lead rises to 12 per cent in first poll since leadership crisis
Back in hung parliament territory
New survey shows Tory lead narrowing to 10 points
Poll finds 57 per cent oppose independence as Salmond prepares to publish referendum plans