It's given in the range brochure. The one I have relates to the 2007 model year but I doubt it changed ... 2424mm, or 2624mm using the area under the seats.
You know the Compact doesn't have room behind the back axle for an under-slung spare wheel, so you have to carry it inside? The Long is only 9.5" longer overall so makes more sense IMHO unless the length is absolutely critical.
The load length for the Long is given as 2667mm at floor level, not using the area under the seats. That's a fair bit more than 8 feet (2438mm), but I guess the rake of the front seats gets you with the sheets upright.