It’s thought that army chiefs developed the technique to ensure soldiers didn’t make mistakes due to tiredness. The technique is said to work for 96 per cent of people after six weeks of practice.

Here’s how to do it:

1. Relax the muscles in your face, including tongue, jaw and the muscles around the eyes
2. Drop your shoulders as far down as they’ll go, followed by your upper and lower arm, one side at a time
3. Breathe out, relaxing your chest followed by your legs, starting from the thighs and working down
4. You should then spend 10 seconds trying to clear your mind before thinking about one of the three following images:
   • You’re lying in a canoe on a calm lake with nothing but a clear blue sky above you
   • You’re lying in a black velvet hammock in a pitch-black room
   • You say “don’t think, don’t think, don’t think” to yourself over and over for about 10 seconds.