//Due to our first past the post electoral system, Labour won 355 seats in the House of Commons vs the Tories 210 seats – so a 9% lead would appear more than sufficient to kick the Tories out.//
Whilst I’m not saying you’re wrong, Hymie, it isn’t quite so straightforward as that. The vagaries of the FPTP system mean you have to take a lot more into account. For example, the 9% lead you speak of may be restricted to seats which Labour already hold, in which case it is of no use at all. Conversely, it may all be in seats Labour does not currently hold, in which case it would benefit them enormously. Either of these is unlikely and the reality is almost certainly somewhere in between. The trick is to find out just where.
And of course this neglects to consider what might happen between now and the general Election.