Wife arrived home last night reporting a squealing clutch when depressed, and potentially a smoky experience when she had to drive along a little lane with lots of clutch required.

I drove in this morning to confirm it.

£500-£600-ish do we reckon?

That sounds like a dry release bearing to me.
You haven't said how high or low your pedal is, which could indicate state of wear on the clutch.
Try to give as much info as you can to help members to help you.
I wouldn't expect to pay that much for a clutch job - mind you, I'd do my own anyway, so it'd cost me only parts.

£318 inc VAT all done. Seemed a fair price, in at 11:30am yesterday and done by this morning, can't complain.

That's a good price. Did they replace the entire clutch for that?

As you've paid out for the clutch, does that mean your earlier post about ditching the Multipla is now redundant?