Only four things really move opinion polls

Last night's polls showing the Tory lead at 5.2% in ConHome's Poll of Polls suggests that 'lobbygate' had no discernible impact on public opinion.

Neither did the wonderful news that Samantha Cameron is expecting a baby.

Neither did the Tory assault on Labour's union links (although it has energised the Tory vote).

Neither did the Lord Ashcroft drama - played out for days on end in BBC news broadcasts and in the pages of the Independent and Guardian.

Neither did bullygate.

I don't say these news events that fascinate us have zero impact. They will impact some voters but they are not decisive in moving votes.

I suggest we need to look at four factors in the weeks we have left before polling day.

The underlying state of the economy and voters' sense of which parties will best protect their household income. The Tories need to put a price on the cost of doing nothing about the deficit. Anthony Wells noted yesterday that most Budgets have hurt Labour in recent years.

The voters' sense of the party leaders. CCHQ, to my mind, is over-emphasising the need to present Cameron as likeable. They need to ensure voters see him as a strong PM-in-waiting. The debates will give him that opportunity. He must not be flippant or negative in those debates. He must look strong, in command, honest.

The unity of the parties. Voters always hate divided parties. Discipline in Tory ranks remains strong but the closer opinion poll gap has also silenced the 'noises off' within Labour.

A winning, believable policy. Few policies move opinion polls but George Osborne's 2007 pledge on inheritance tax caused a political earthquake. I've long believed that the party's good policies on immigration will move voters but it is now getting too late to talk about the issue.

Tim Montgomerie