Our model now gives a 7% chance that the Conservatives will be the largest party but could only form a majority with the support of all of the Lib Dems, the DUP and UKIP. But the Lib Dems would also be able to form a majority with Labour and the SNP. In our central forecast, the Tory-led group would have 325 seats while the Labour-led group would have 338.

We had previously assumed a four-way deal for a very slim majority involving both the Lib Dems and UKIP very unlikely, and that this scenario would therefore result in a Labour-led government supported by the Lib Dems and the SNP.

However, the Lib Dems are keeping their options open. They’ve refused to rule out a deal involving an EU referendum – UKIP’s key demand – and have suggested they’d give first refusal to the largest party (in this case the Conservatives), while saying they might still be willing to work with the second largest (Labour).

We are therefore now designating this outcome the “Lib Dem kingmakers” scenario. So our model now points to a 47% chance of a Labour-led government, a 46% chance of a Tory-led one, and a 7% chance it’d depend which way the Lib Dems go.

Date of forecast: 21 April 2015
Days till the election: 16

Inputted current average poll shares
Con: 34%
Lab: 34%
LD: 8%
UKIP: 13%
Others: 11%

Forecast GB Vote Shares (with 95% Prediction Intervals)
Con: 35% (31% – 39%)
Lab: 33% (29% – 36%)
LD: 10% (6% – 14%)
UKIP: 12% (8% – 16%)
Others: 11% (9% – 12%)

Forecast Scotland Vote Shares (with 95% Prediction Intervals)
SNP: 47% (43% – 51%)
Labour: 28% (24% – 32%)

Forecast GB Seats (with 95% Prediction Intervals)
Con: 288 (246 – 331)
Lab: 263 (221 – 302)
LD: 24 (16 – 33)
SNP: 51 (42 – 57)
PC: 3 (2 – 3)
UKIP: 4
Grn: 1
(May not sum to 632 due to rounding of sums of probabilities.)

Central forecast: Con short of a majority by 35
(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 most votes: 73%
Lab most votes: 27%

Con most seats: 69%
Lab most seats: 31%

Hung Parliament: 91%
… with Con largest: 60%
… with Lab largest: 31%

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

Con majority: 9%
Con+DUP: 6%
Con+LD: 17%
Con+LD+DUP: 14%
Con largest, Con+LD+DUP+UKIP or Lab+SNP+LD maj: 7%
Con largest, but Lab+SNP+LD maj: 11%
Con largest, but Lab+SNP maj: 4%
Lab largest, Lab+SNP maj: 8%
Lab+LD+DUP+SDLP+PC+Grn+Hermon: 7%
Lab+LD+DUP: 7%
Lab+LD: 7%
Lab+DUP: 1%
Lab majority: 0%

(Probabilities may not sum due to rounding)