Grrr not simple sadly.
It has loosened itself off again.
The only thing i've noticed that is dodgy is the chainring isnt central on the crank so there's a definate slack spot then the chain tightens to the point you can feel it through the pedals.
Also the chainring is pretty big so i'm having to put quite a lot of torque down.
Could either of these issues cause the problems i'm experiencing (ie the hub unwinding itself)