If you want to keep your turf looking as good as possible, rake them up and bag them. Last Friday's Gardener's World on BBC showed how to use them to make leaf mould, a good soil enricher. If you missed it, try watching on i-player maybe? Get someone to help you rake leaves if it seems to daunting on your own, it would be more fun and quicker that way.

Yes, they will damage the grass if left - they'll exclude light and air, and sit there as a soggy mass, so the effect is the same as if you'd left, say, a paddling pool in the same position for longer than 2 weeks.