Sky Europe did it and so have other airlines that over the years moved flights to Luton from other London airports. Ryanair often shifts flights between airports to save a few pennies, in fact they started life flying to Gatwick before moving to Luton and then moved the majority of their London operation to Stansted.
Also look at BA, they used to have a major operation at Gatwick and even now are still moving routes out of Gatwick to Heathrow when they can find a slot.