Parachute club in Oxon. Stretch Cessna (dunno what model, first and only time it visited) had been doing static line lifts all day. Finally a free-fall lift. Everyone and their dog gets on board. I'm sitting on floor with back to pilot's seat. As usual everyone scrums forward to put CG forward - old lag skydiver practically lying on top of me gripping back of pilots seat. Off we go down the grass strip - but something's not quite right - we pass the bump in the strip where an aircraft normally becomes airborne still firmly attached to terra firma.Old lag on top of me looks distinctly worried. End of strip runs into an adjoining field - but small matter of large hedge, shipping container and landrover in close proximity. Pilot hauls back on stick and we stagger into air accompanied by stall klaxon. Clear hedge etc but not really climbing. Everyone remains firmly scrummed forward looking somewhat nervous. Oxfordshire still seems very close below. Finally, taking what seems like an age, we gradually edge up to 2,500ft. Most of the lift had asked for a higher exit but, curiously, everyone seemed anxious to get out as soon as possible.