got an aerosol car in Halfords, bog standard upholstry cleaner, nothing swanky. Using it and a (clean) washing up brush I scrubbed the seats and they came out great, light coloured fabric with all manner of juice, bikkies, chocolate, yoghurt stains (I'll get those darned kids ...as they say in Scooby Doo !!).
New buyer said the car was immaculate (as it was). Will post the name of the cleaner tomorrow but a DIY job is more than sufficient.