IT'S ALL IN THE GEOGRAPHY
The Conservative Party opposes proportional representation, but the first-past-the-post electoral system which has underpinned British politics will ensure that they will struggle in the election.
This is because Britain's electoral geography is tilted heavily in favour of Labour. The Tories need many more votes to win the same number of seats. Labour now reap the benefits of a system which penalised them in the Eighties.
The easiest way to look at electoral bias is to see how many seats either party would get if they had got the same number of votes and the Lib Dems repeated their 2001 performance. In this scenario, using data from a recent You/Gov survey, in 2005 Labour would win 364 seats, 140 seats more than the Tories and the Lib Dems would be down to 43.
If both Labour and the Tories had 34% support, Labour would have 343 MPs and the Tories 20, giving Tony Blair a majority of 40. If there were no bias between the two main parties, each would have 272. This means Labour's bonus is worth 71 seats.
There are two main reasons why. First of all, Labour enjoyed above-average swings in the last two elections - the seats they won in 1997and those they retained in 2001.
Had the votes gone as they had in the rest of the UK, Labour would have had 40 fewer seats today. Also, the Lib Dems had above average swings in the Tory seats they were targeting, shifting 15 to 20 seats into their column.
More significantly though, Labour constituencies have on average 6,000 fewer electors than Tory ones. This is because boundary changes do not keep up with demographic changes where people gradually move from Labour strongholds in the cities to Tory strongholds in the counties. This is worth about eight seats to Labour at the Tories' expense.
So, in a nationally tied election where Labour and the Tories both scored 34% of the popular vote, the average Tory MP would have 22,000 votes compared with the Labour MPs' 16,000.
Average turnout in Labour constituencies (57% in 2001) is also lower than in Tory ones, (63%) so Labour MPs simply need fewer votes to win. This is worth about 10 extra seats to Labour, at the Tories' expense.
But basic geography hits the Tories hard. Scotland, a Labour stronghold, is over-represented with 55,000 electors per constituency compared with 70,000 in England.
Even if the two main parties level pegged there, Labour would still have an additional an extra nine seats, the Lib Dems two and none for the Tories. Wales is also over-represented, with 57,000 electors per seat - worth an extra four seats to Labour.
So it likely that Labour can retain its lead even if it lost the popular vote. A YouGov/Sunday Times poll projected a Labour majority of 86, where they would lose 37 seats even though its lead in the popular vote would halve to 4%.
In concrete terms, Labour could end up with over half the MPs in the Commons, but at 36% popular support, non-Labour voters would outnumber Labour voters by two to one.