Labour and the Tories remain just a point apart in our polling average: 33% to 32%. The Lib Dems are down 1 to 8%, while UKIP gain a point to 15%.

But, with more polls showing the SNP leading by a big margin in Scotland, the main change from last week is an increase in the number of votes and seats we expect them to win. Our central forecast now has the SNP taking 43% of the vote in Scotland to Labour’s 29% – up from 40-29 last week – and winning 41 seats, up from 36.

That dents Labour’s (already low) chances of a majority, from 9% last week to just 6% now. The Tories are still clear favourites to win the most votes (we give them a 71% chance), but only very slight favourites to win the most seats (with a 53% chance), and their chances of securing a majority are still just 12%. The chances of a Hung Parliament are, therefore, up from 79% to 83%.

So it’s an improved forecast for the SNP and a slightly worse one for both Labour and the Lib Dems. That makes it more likely that Labour (plus, if necessary, the minor left-wing parties) have to rely on the SNP for a majority. Our model puts the chances of that combination (without the Lib Dems) at 20%, up from 12% last week.

Date of forecast: 23 January 2015
Days till the election: 104

Inputted current average poll shares
Con: 32%
Lab: 33%
LD: 8%
UKIP: 15%
Others: 12%

Forecast GB Vote Shares (with 95% Prediction Intervals)
Con: 33.9% (±5, i.e. 29% – 39%)
Lab: 31.2% (±5, i.e. 26% – 36%)
LD: 10.4% (±5, i.e. 6% – 15%)
UKIP: 13.6% (±5, i.e. 9% – 18%)
Others: 10.9% (±2, i.e. 9% – 13%)

Forecast Scotland Vote Shares (with 95% Prediction Intervals)
SNP: 43% (±5, i.e. 38% – 48%)
Labour: 29% (±5, i.e. 24% – 34%)

Forecast GB Seats (with 95% Prediction Intervals)
Con: 283 (233 – 339)
Lab: 278 (224 – 324)
LD: 23 (13 – 38)
SNP: 41 (26 – 51)
PC: 3
UKIP: 3
Grn: 1
(May not sum to 632 due to rounding of sums of probabilities. Prediction intervals not yet available for UKIP, PC and Grn.)

Central forecast: Con largest party, but short of a majority by 40
(Criterion for majority now changed to 323 not 326, assuming Sinn Fein win 5 seats and do not take them.)

Probabilities of key outcomes
Con largest: 53%
Lab largest: 47%
Hung Parliament: 83%
… with Con largest: 41%
… with Lab largest: 42%

Probabilities of predicted government outcomes:
(See here for explanations and assumptions)

Con majority: 12%
Con+NDown: 1%
Con+ND+DUP: 6%
Con+ND+LD: 9%
… with Con+ND+DUP also possible: 6%
… without Con+ND+DUP also possible: 3%
Con+ND+DUP+UKIP: 0%

Lab majority: 6%
Left (Lab+SDLP+PC+Grn): 3%
Left+LD: 24%
… with LD as kingmakers: 0.5%
… without LD as kingmakers: 23.5%
Left+SNP: 44%
… with Left+LD also possible: 24%
… without Left+LD possible: 20%
Left+SNP+LD: 25%
… with LD as kingmakers: 24%
… without LD as kingmakers: 1%

LD kingmakers: 24%
With a choice between Con+ND+DUP(+UKIP)+LD or
…Lab+SDLP+PC+Grn+LD: 0.5%
…Lab+SDLP+PC+Grn+SNP+LD: 24%

(Probabilities may not sum due to rounding)