If you scroll down to yesterdays questions you will find that members answered a question on clay soil, good luck.

Or to save you searching, the answer is to incorporate as much humus rich material as possible - this means things like garden compost, soil conditioning compost from the garden centre or your local recycling centre, spent mushroom compost, leaf mould, well composted manure, things like that, plus horticultural grit. It will take time to make a difference, and the humus rich stuff should be incorporated every year if possible, twice a year if you can, spring and autumn.

I agree with Bamboo. And I know from experience that it is almost impossible to do all at once, we have clay that you can make pots from! I don't know if this is the correct thing to do but, this has worked for me...every time you plant something, dig a much bigger hole than necessary ( I have to use a pick axe!). Mix some of the soil with an improver, then backfill. Then plant the plant with planting compost around its roots. I have always put small bark chippings on top, some of which end up in the soil and are replaced...it seems to help.

or you could go with the flow and builda natural pond or at least a lovley bog garden .