Unlike in Scotland (and I believe the USA), there is no set interval between elections for Westminster. We're all assuming the next Westminster general election will be in 2009, but that isn't necessarily so.
I've heard a very reasonable-sounding theory that Gordon Brown may intend to call a snap general election in the autumn of this year, if the opinion polls suggest that Labour is in a favourable position at that time.
I can see the logic. New leader may lead to a "honeymoon" increase in the Labour poll position, and taking advantage of this to gain his own mandate, and at the same time put off the need to go to the country on his actual record until 2011 or 2012, does have its points.
Rolfe.