Renault Kangoo loud rattle when in gear

as i drove van out of my drive on to road there was a loud bang ,then a rattle/grinding sound .
. the van then stopped dead at 10mph, as if the gearbox had locked up. managed to get back into my driveway in 1st gear, the engine runs fine but will stall when in neutral if pedal is not pressed in. there is no rattle sound when pedal pressed. van drove fine prior to this problem.