Following everybody's advice yesterday I filled up the clutch reservoir today (it was empty) ran the engine for a while and pumped up the clutch pedal, after a while the spring was back in the pedal and the gear change was back to normal. Ran it around for a while and everything seemed OK but I'll ring the garage tomorrow presumably they'll need to check the system has no leaks.
Special thanks to Linotype for your long distance advice, as good as having you next door!
Not 100% sure about an Honda HRV, but some hydraulic clutch systems need to bled ( pretty much like bleeding the brakes ), could be that the bleed nipple has loosened causing it to lose hydraulic clutch fluid everytime you change gear.