Best leaves for the compost heap are beech, hazel, hornbeam. One to avoid is sycamore as toxins are retained in the leaf which actually are prevent germination and/or retard growth. (Look up allelopathy). Oak takes a while to rot down, too, but otherwise practically all leaves from deciduous trees are fine .

Also the leaves of a walnut tree are like leather and takes ages to rot down,(talking from experience).

The leaves from Sweet Chestnut take ages to rot (unless you can put them through a shredder), I'm also talking from experience!

Hortum this is terrible news. I have masses of sycamore, mixed in with a bit of ash. But I've been using it for a number of years to improve my soil and things do seem to be growing OK.

Sycamore just needs a couple of years rotting to ensure its done with its negative approach to the world's seedlings. It's ok after that. It's the most recently composted ones which still harbour a grudge. Almost any composted material is good after a couple of years. My brother called me just yesterday to tell me that a 20ft by 6ft high pile of twigs/small branches he'd stuffed into a corner with his digger has rotted down over the last three years and he's just spread it across his veg patch like soil. It's all ultimately organic and useful. What's important is that we do more of it, and less of the chemical bit, in my opinion.

Ah, that explains it. Thanks for the reassurance! Do you happen to know what it is in the leaves that does the damage?