I have a very vague recollection of coming across a scenario ( but am open to correction) where employers 'provide' a creche but do so in a manner which looks a lot like outsourcing, which is in practical terms not that different to paying creche fees, but which benefits from the favourable tax treatment.
This particular tax treatment has always struck me as quite unfair, in that it makes it impossible for small employers to compete with larger ones in offering this benefit.