New member from bournemouth help with micra problem

Hi I'm Paul from bournemouth, I've got a 1994 silver micra 1.0l k11 with only 50000 miles on the clock.
It's developed a fault when I'm driving in 4th or 5th gear accelerating reasonably hard the engine revs up like the clutch is slipping.
I've done the clutch test by sticking it in 5th gear and stalling the car which it does without the clutch slipping so I'm not sure if it's would be the clutch.
If anyone has any ideas would be greatly appreciated thanks.
Adjustment on the clutch possibly

Clutch may be worn, mine start slipping when the clutch is warm, let it cool down and it's fine