How big is the pond? If it's large (at least as large as Monty Don's) I think I'd let it invade a little way, but keep an eye on it. If it's smaller than that then personally I'd get rid of it and make sure you've got plenty of good marginal plants. Creeping buttercup can make itself into a sort of a raft and eventually the roots will take over the pond which will silt up - I've seen this happen in old ponds on commons etc, once the cattle stop wading into the pond to drink.
On second thoughts, I'd take the buttercup out, even if your pond is as big as Monty's.
Some Marsh Marigold might be nice to replace it