4s flashlight is on, icon is greyed out on control centre and it will not switch off. Any ideas?

[iMore Question]

Torch/flashlight was used last night. Been out for a walk in the rain with phone in a sealed pocket. Torch is now on, flickering and won't switch off either with homepage shortcut or control centre and the torch icon in control centre is greyed out.

 

[kch50428]

Hold the home & power buttons until you see the Apple logo...then release the buttons and let it reboot...