Ok first thing to do if you find you cannot open the bonnet....
Method works for both Laguna I + Laguna II..
Whilst pulling on the lever - have a friend, wife, largish child, mistress, passer by etc etc etc - push down on the centre front of the bonnet..
This will over come all but the dreaded snapped cable..
Once open apply general purpose car grease to the catch mech and strike plate..
Or next time your at a friendly garage ask them if they could pop a little grease onto the bonnet catch for you..
Be catious not to enter the realms of unsubtle sexual inendo whilst requesting this "extra"..