If Britain had retained Heligoland

What effect would British possession of Heligoland have had in the world wars?

It would seriously complicate German naval operations, but Britain would face intense attack and a difficult resupply problem, especially in the Second World War.

In the First World War, Germany would need to assault or isolate the island, turning it into a persistent problem at the mouth of its naval bases. In the Second, air attack would make the position still harder to hold. Submarine resupply might become necessary if the Royal Navy insisted on retaining it.