Folks,
I live next to a former sandstone quarry and so you can imagine what my soil is like. Twice this year I've had to pump out the garden from flooding which isn't good news BUT....
I have transformed borders and the veg plot beyond all imagination using a combination of a few simple things. After searching on the internet and digging up some old papers written on the subject of clay soils - some > 100 years old I have used the following;
Sharp sand - not much needed really a good covering and dig in.
Horse muck - 6-8inch layer over winter and dig in.
Coffee grounds - just add when you can get them from Starbucks, Costa etc.
Hops - local microbrewery has helped out here.
Where I could, I have dug out the clay with a pick axe and shovel and replaced it with whole bales of straw and replaced the topsoil.
The coffee seems to have an immediate effect on helping to break up the clods and the hops and sharp sand improve drainage by leaps and bounds whilst still retaining moisture.
My soil tempertaure is much better, and despite the flooding the veg patch and the borders drain almost immediately.
The lawn is the biggest drainage issue, if I had my way I would dig it out and repeat my cure - more room for the veggies too!!
You do have to watch the pH though - all this organic matter can push you to the acid side and doesn't really help the veg.
2 years ago I struggled to turn the garden with a small spade, I can now plunge my arm into the veg patch almost up to my elbow and I've never seen so many worms!
Best of luck,
Make do.