Humus rich materials, like organic soil conditioning compost from the garden centre, home made compost from the heap, leaf mould, spent mushroom compost, compost from your local recycling centre, well composted horse manure, as much as you can get hold of, dig it in or lay it on the top. Some sharp grit from the garden centre would be useful too, to help open up the clay structure. Sand won't be very effective.

Compost, compost, compost. and Mulch mulch mulch......I suffer the same here. Sharp sand but not too much and only add it along with your organic matter. I don't know if you are allow to over there but adding gypsum helps break up the clay and bind it to the organic matter. A thick layer of mulch will stop the clay from compacting and bring the worms up to the surface. The worms will help aerate the soil and pull the organic matter down. It is an ongoing process so keep on doing it for the rest of eternity!! LOL

I have used gypsum, don't know if its still available, but it can't be used where plants are already growing, well, not in sufficient quantity to make much difference.

Really Bamboo??? I've added it around my plants and haven't seen any problems. Mind you, I just scatter it on. You do have to add it along with your organic matter though. Not on its own.

I can't remember what it does now, it interferes with some chemical exchange process - in order for it to be effective on heavy clay (and I know that's what you've got, I've seen it in your blog!) it should be used in a certain ratio, which is much more than any plants growing there could take. On the other hand, if you have a bed that's empty and won't be planted for a while, it's a good thing to use in the right amount. I might be obliged to go and look up my old training notes - or not!

Well, most of the time I can't afford it Bamboo.....I garden on a budget. I have 5 compost bins and mostly just compost....compost....compost.

I have heavy clay too, and it has taken several years to get a good depth of lighter, workable topsoil. I find grit is the best thing for opening it up and usually invest in a couple of bags or so in autumn. I also dig or scatter any compost I have made in spring and grab any horse manure I can find at any time!