I'm with Woody on this one; apart from the surveyor being more of a valuer, I don't think he's got the right idea, and you need another slate worktop installer to check it out. Have a chat with you're local Magnet store, and see if they know someone to come out, and offer a bottle of scotch for their time.
The pictures give us a general idea of what's happened, but doesn't clearly show why. There is a disparity in the heights of 5mm, so one of them has dropped, but as it shouldn't have done so by that much, it suggest that the kitchen base unit may have dropped on one side as well. Put a level on both sides, and across it, and find which side is out. It may be that the work top needs removing, the kitchen units re-levelled and supported underneath with blocks, and a couple of metal struts fitted across the base unit to provide support for the joint, but a butt joint should have been fitted over the carcase edge, not in the middle of a unit.
The supplier hasn't chased the debt, and the judge will pick up the implications of this, and he will realise that the worktops cost more than £900 to supply and install. Drewjak has been trying to resolve this for some time, so getting to court after 6 months is a natural progression, and still in his favour. And I can't see the fitter trying to counter claim for £2500, as it'd open a can of worms for him, and yes, definitely check for CCJ against him.