it would tilt and it would slide using the handles but not the full tilt forwards and slide forwards mechanism.
had it out today and was surprised at the quick fix!
thought I'd share in case others have the issue:

basically the rear of the seat is joined to the slide rack via a cable system. the cable is pulled when the seat rear tilts forwards, engaging the slide mechanism.
the round silver pin located top centre of the image shows the end of the cable mechanism on the base of the seat. follow that back and down to the base of the seat back.
on mine the blue locking lug:

had slipped out of its locating hole meaning there was nothing to allow the seat tilt to pull the cable. the cable itself is locked into the seat rear via the bent metal section bottom right of the picture. if your seat is stiff even with the fix in place its probably possible to adjust the tension at this point with a pair of pliers and simply bending that metal lug area tighter; this should increase the amount the slide mechanism locks are disengaged
relocated the lug, greased and oiled it all and job done!!
hopefully this might help someone else!