This has been a relatively good week for the Conservatives in the polls. But they will have to make more progress yet – or hope that some of the pollsters at least are wrong – if David Cameron is to retain the keys to Downing Street.

Our latest poll of polls, based on all of the polls published in the last week, puts the Conservatives ahead for the first time in the campaign, albeit only by one point. The party’s support has edged up to 34%, while Labour remain on 33%.

However, on its own a one-point lead will not necessarily be enough to make the Conservatives the largest party. Thanks to the failure of the party to get the constituency boundaries redrawn, Labour voting seats contain fewer registered voters than Conservative voting ones, while the turnout in Labour seats tends to be lower too.

Are you undecided about who to vote for on 7 May? Are you confused about what the parties stand for and what they are offering? Take this interactive quiz to help you decide who to vote for...

As a result, and despite Labour’s continuing difficulties in Scotland, the party could still win 290 seats to the Conservatives 275. The balance of power would be held by 50 nationalists and Greens, who are committed to voting Mr Cameron out of power.

However, this assumes the swing to Labour in the key Tory-held marginals matches the 4% swing the polls currently anticipate across England and Wales as a whole. But this may not prove to be the case.

In pictures: Experts' predictions for the General Election - 26/04/15 Show all 10 1 /10 In pictures: Experts' predictions for the General Election - 26/04/15 In pictures: Experts' predictions for the General Election - 26/04/15 Andrew Hawkins (ComRes) “This is an election of wild promises and political cross-dressing; so no differentiation, no breakthrough, no majority. The most likely outcome is Ed Miliband in No 10 because only he will be in a position to work with enough parties (that is, the SNP) to form a workable government.” Andrew Hawkins In pictures: Experts' predictions for the General Election - 26/04/15 Joe Twyman (YouGov) “As each day passes and the Conservatives fail to increase their vote share, the likelihood of Ed Miliband becoming PM (albeit still with a minority) grows. That’s due to the continued performance of the SNP in Scotland and former Lib Dem voters propping up Labour in England.” In pictures: Experts' predictions for the General Election - 26/04/15 Ben Page (Ipsos MORI) “A better week for Ed Miliband than for David Cameron – personal ratings improving, and the betting markets moved in his favour. The poll numbers have him ahead by a whisker which, combined with the electoral maths, makes him more likely to be able to form some kind of government on the raw numbers right now. However, Cameron will be hoping for a 1992 moment when ultimately voters can’t quite bring themselves to try someone else – and 38 per cent of voters still say they may change their mind.” In pictures: Experts' predictions for the General Election - 26/04/15 Rick Nye (Populus) “The Populus/Hanover Predictor has Ed Miliband ending up as Prime Minister in more than five out of six simulations we run.” In pictures: Experts' predictions for the General Election - 26/04/15 Nick Moon (GfK) “Tories most seats, SNP 45 or more, Ukip fewer than five: minority Labour government.” In pictures: Experts' predictions for the General Election - 26/04/15 Damian Lyons Lowe (Survation) “Ukip’s vote share is prone to be squeezed, benefiting the Conservatives, while the SNP’s onslaught on Labour continues. Based on three UK/Scotland polls, I am upgrading the Conservatives and the SNP, and downgrading Labour. Both the Lib Dems on 30 seats and Ukip on 5 to 10 remain unchanged.” In pictures: Experts' predictions for the General Election - 26/04/15 Michelle Harrison (TNS) “Still no change, but Nicola Sturgeon goes from strength to strength in Scotland. For me, who the biggest party is will hinge on the crucial marginals. But what ultimately wins – safety first, for the Tories, or Labour’s ‘get out the vote’ ground war?” In pictures: Experts' predictions for the General Election - 26/04/15 James Endersby (Opinium Research) “Our poll today shows a one-point Tory lead, statistically a tie. It’s going to be incredibly tight. Labour and the Tories would do well to be negotiating with the smaller parties behind the scenes. In the likely event of a hung parliament, we’ve been testing various combinations of coalition. Labour teaming up with the Lib Dems would be more popular than with the SNP, which in turn would be more popular than a Tory/UKIP scenario.” In pictures: Experts' predictions for the General Election - 26/04/15 Martin Boon (ICM) “Not much going on really, and no reason to change my mind. Tories by a couple of points. In pictures: Experts' predictions for the General Election - 26/04/15 Lord Ashcroft (Lord Ashcroft Polls) He refuses to make predictions. “My polls are snapshots, not predictions.” Rex

A poll of Tory held marginals conducted by ComRes this week suggests the swing to Labour could be between a half and one point lower in Tory held marginals. Lord Ashcroft’s polling points to a similar conclusion, at least in those marginals being defended by an incumbent Tory MP for the first time.

If the swing to Labour is a point lower in Tory held marginals, Labour’s projected seat tally, at 277 seats, slips below that of the Conservatives on 279 - though the nationalist block would still be able to keep the Conservatives out of power.

But there is an important discrepancy between the polls. Those conducted by phone, which have very much been in the minority, have on average since Easter put the Conservatives three points ahead. In contrast the two parties have been tied on 34% each in internet polls

Unlike a one-point lead, a three-point one would be sufficient to put Mr Cameron clearly in pole position. Much rests on which polls are right – and on the last week.