play fast and loose ignore your obligations; be unreliable.

☞ Fast and loose was the name of an old fairground game, in which a punter was challenged to pin an intricately folded belt, garter, or other piece of material to a surface. The person running the game would inevitably show that the item had not been securely fastened or made 'fast', and so the punter would lose their money. The phrase came to be used to indicate inconstancy.

2013Daily Telegraph It seems the First Minister has been playing fast and loose with the facts on EU entry and has been spectacularly caught out.