You don't tug at an apple to remove it, place your hand under the apple lift it slightly and gently twist, the apple should then come away in your hand.

Thank you Moon growe I don't usually "tug" but have tried that in desperation! We inherited this tree along with two other apple trees 11 years ago and this is the first time I have had trouble harvesting the granny smith, the others, though a bit later this year were picked without trouble. I can only guess that they are not yet fully ripened and fear the frost will spoil the crop before we can gather them.

You could try snipping the apples off with a pair of secateurs and then put the apples in a drawer with a ripe banana to help them ripen - nothing to lose!