Bookies predictions for seats won in UK 2015 General Election

Here is the mean of bookies predictions for seats won in the UK 2015 General Election plotted over time:

Bookies predictions for seats won in UK 2015 General Election

These values were collected by repeatedly scraping bookies websites for odds given for various bands of seats for each party, eg:

As I type this Ladbrokes is giving 7/4 odds for SNP getting 40 to 49 seats in Westminster.

Each of those odds is turned into a probability, the mean of each party/band is then amalgamated to give a number of seats which the bookies as a gestalt think each party will win.