Election 2015: Why David Cameron will remain as prime minister

Since Adrian wrote this article, he has amended his predictions. See his latest view here.

We now have only four weeks to go until the election. Last time, I noted that I expect David Cameron to still be prime minister come 8May, and today I'm going to explain to you why. It's a simple matter of electoral arithmetic.

Take the latest odds, which come following the seven-way leadership debate. The spread' on seats has hardened to 284-88 (Tory) and softened to 269-73 (Labour). The SNP are marginally better (41-43), Ukip are unchanged (5-7), but the LibDems have weakened notably (23-25).

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Bookies report that the expected weight of money is yet to come: not much of a surge' has been seen so far.

To win a majority, a government or coalition needs to take 323 of the 650 seats (I'm excluding Sinn Fein, who are expected to win six seats, but don't take them up or vote). Also, the incumbent prime minister has the first shot at forming government, which could be a very significant advantage.

So at the current offer prices (ie the higher of the two figures in the spread), you'd have the Tories and the LibDems on 313. If they then throw in their lot with Ukip and the DUP, who are expected to win 14 seats between them, you'd have a majority of 327.

On the other side, you'd have Labour plus the SNP on 316. If the DUP join their coalition, that would make it up to 323. But Miliband has ruled out a coalition with the SNP, as have the LibDems.

So in all, it still looks as though a Conservative-led coalition is the more likely outcome.

As it is, I also expect the Conservatives to win more seats than the bookies are pricing in at the moment primarily due to the big shift in Scotland. Come the big day, here's how I expect the results to pan out.

Under this scenario, Tories and the LibDems remain in coalition, with 302 seats and 31 respectively a comfortable majority at 333. Although if necessary, they can add in Ukip and the DUP for another 11 seats, taking them to 344.

A Miliband-led opposition, composed of Labour (on 248 seats) and the SNP (on 40), would have 288 seats between them. Even if you add in SDLP, Plaid Cymru and others, that's still only another 11 seats, for 299 (remember the Speaker and Sinn Fein do not use their votes).

So if the voting goes the way I expect it to, then only Cameron can form a government, even although it's likely to be in coalition with the LibDems again. In no way can Miliband command a majority.

Adrian Sykes will be writing regular election commentary on the MoneyWeek website between now and 7 May. If you enjoy his columns, sign up to our free daily email, Money Morning, below, to be alerted to when a new one is on the site.