Cheers Gareth
It's not roof related as far as i can tell, the water only ever appears in the drivers side footwells - front and back!
Carpet removal seems the next step - don't know if I have the patience/skill to do it.
The odd thing is that when I got in it this morning (rained heavily last night) the carpet seemed dry, but when i set off the water seemed to rise! It's not heating/cooling associated as it only happens when it rains heavily - hence my thought of blocked drains.
I read a post about drains from the rear, around the roof box - any idea on location of those??