Posted: 27/08/2013 at 10:56
morning mark.. welcome to the forum
i would add manure to the soil as it is then trench and mix it all in together, I would dig a trench 30 to 40 cm deep, loosen the clay at the bottom of the trench with a fork and infill with the manure, sand and clay. when done I would add your topsoil, making sure it is good stuff, and lightl;y scratch it into your existing soil mix.
one more word though....do you think you have any drainage problems? does water seem to drain away fairly well? When you trench you will have a sense of how wet or not your soil is anyway.
good to get rid of that artificial turf. good luck