Personally, I'd wait until October/November and plant up either bare root or pot grown plants...make sure the ground is well prepared and free draining.
...If you're using a single line 6" apart then you can take out a continuous trench for planting into which will make it easier.
Hope this helps.
Thank you so much for responding to my never ending questions! Upon your sound advice, I have decided to wait until Oct/Nov and meanwhile have sourced well rotted manure (thank you mr knowles!) to cultivate the soil.. the trench has been dug so I'll be taking care of the ground now in preparation of the privets - have opted to go for a single line now. How wide and deep should the trench be? (at the moment its about a foot wide, and ive taken quite a bit of soil out so that i can mix manure in there) how deep should i dig?