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.