It does like a free drained position and will hate an over moist bed. It grows as an an under storey shrub between larger evergreen trees in several parts of warmer souther Europe and around the Mediterranean.

I note you're in Essex - whilst you've planted it somewhere "moist", if your area's anything like west London, you've had no decent rain to speak of for weeks - check that the rootball isn't completely dried out, and that the soil around hasn't also dried out. New shrubs and trees need to be kept watered until they're established.