It sounds like a dry piston and pedal box scenario, usually down to hot days on motorways where the clutch pedal isn't used as much.
The accelerator pedal could be just a coincidence due to the heat and dry air around the foot well due to air con.
Try this.... Buy a spray tin of silicon lubricant spray (much better than wd40 and lasts a lot, lot longer).
Seat all the way back, and with a torch get your head into the foot well. You will notice the clutch pedal is attached to a long metal bar via a split pin and then goes into a cylinder with a rubber boot attached... First spray around the split pin that attaches to the top of the pedal.
Using the straw attached that comes with the spray can, carefully insert the end of it inside the rubber boot and move the straw top to bottom inside the boot, while you spray... Give the pedal a good few presses to make sure the metal rod is getting a good coating.
Now do the same to the top springs of the accelerator and brake pedal, pay attention to the accelerator top clip... Just be careful not to get too much spray on the pedal rubbers for safety reasons....
Don't worry if it gets on the carpet, it is safe to use on materials and will dissipate without staining (unlike wd40)
Repeat this process every three month or so to keep it in tip, top condition
Hope this helps