Thank you for all responses. Chesty Morgan, are you referring to Callerton Hill, which is at the end of 25? I know that aircraft have to be 'light enough' to safely clear the hill when climbing out.
The hill poses no problem for take offs, most aircraft (even the emirates 777) pass this at ease with 2000ft to spare.
Could it be that 07 has a preferred "overshoot" area than 25. 07 being flat and level into a farmers field (notwithstanding the B road), whereas 25 would have to clear an embankment, a railway line and a major trunk road just west of the airport.