Other place it maybe worth asking for advice could be your local bus company depot - see what they do to clean bus seats when they need a heavy clean.
Also maybe you can hire this sort of thing
www.karcher-center-trafalgar.co.uk
Moquette is noted for being robust so it should be possible to subject it to decent cleaning without damage, but if the fabric is damaged (and sunlight light can cause damage/ frailty - often the reason curtains fall apart for example) heavy cleaning or hot water type treatments could cause fabric to tear / fall apart.
Occurs to me London Transport museum, might also be a place to ask.
also useful advice here I'd think
Whether it's fabric, leather or velvet, keep your sofa looking its best by getting the cleaning just right
www.idealhome.co.uk