Just to clarify, you keep saying it was just idling, does the engine still rev up, or does it idle even with WOT?
It does sound like your clutch has let go to me. Being hydraulic they can auto adjust until you completely run out of friction material, at which point they just drop off the cliff. Although I've not had many cars to work on that used a hydraulic clutch where that happened (two of the 18 hydraulically operated clutches I've replaced), but I have come across vehicles where it happened.
Unfortunately the only way to check is to pop off the gearbox, which is a 5 hour 30 minute job, start to finish (using book times), so will cost a few pennies at a garage.