Yep, as late as humanly possible! Less chance of unnecessary intervention then

And if your waters break, it is actually pretty safe to just wait it out for up to 72 hours (according to NICE guidelines) if you take the usual precautions to prevent any infection:
Don't put anything into your vagina, don't immerse yourself in water (bath or spa) if not in active labour, keep an eye on your temp, and dose up on garlic, vit C to help boost your immune system.