Just to expand on a couple of points

1 - I'm told that Protectacoat will remove 'loose / blown' render and
pebbledash and dub it out to the same thickness; then they apply a base
coat of fibreglass resin based render; on top of this goes a trowel
applied layer which is then rollered to give a 'decorative' effect.
There is no indication of the thickness of this coat.

2 - The inside of the wall is definitely damp but whether this is
condensation or saturated masonry I can't really tell.

Thanks everyone for your comments; you've crystallised my reservations
about the wisdom of using this process.

Paul