I know Elstree well the upslope is quite steep on 26 ok for takeoff other than the initial steep start so slow acceleration but because of the trees difficult to use on landing! Also remember on 26 the rest of the runway is uphill albeit only slightly compared to the steep unlicensed bit!
So overall your takeoff distance will not meet level book figures!
On the 08 departure the steep unlicensed but will be near useless but you will get a downslope on the rest if the runway with a wall if trees in front of you
Pace