In terms of leg room it's a total different thing: The LC is much more comfy. In a Landcruiser one doesn't always have to sit straight upright like a british soldier. Also there is more space to the side. Landcruiser owners even find space to fit armrests and cupholders.
The space in the back is not that much different. A Defender 90 is somwhere between a Landcruiser 70 and a MWB 73. A Landcruiser 75 about same to a Defender 110, I guess. Maybe a Defender 130 is slightly bigger than a Landcruiser 76/78.

(Not sure, haven't compared the figures).
Just gut feelings from what I saw on friends' Defenders.
If you seriously consider switching: Go find a Landcruiser to visit for direct compare and hands on experience.
Cheers Ralf