hairspray as recommended by those not allowed spanners

Handlebar grips need a proper bond and there's no need for any reassuringly expensive glues such as Renthal's quick bond or Gorilla's monkey glue to achieve that. The trick is obvious and that is to clean both surfaces and, to be sure, to be sure, rough up the handlebar a little to give a good key to bond to. Then it's down to what you whatever you have to hand, apart from hairpsray, virtually any cheap as chips super glue will do, my weapon of choice would be a RTV silicone.