Many thanks for all your comprehensive replies.
I posted a reply last Monday, or at least I thought I had!?
The boss won't allow any weedkiller as the plot is organic. My hope is that the cardboard is a quick way to smother the least active weeds but it does need some sort of covering (soil, bark etc) to keep the light out completely. I will spend this summer digging out anything that comes up (and a few more summers no doubt) then sew seeds in the autumn or next spring.
Thanks again to all, I think Watery perhaps points me in the direction I was hoping for. I'll let you know how it works out.
I still don't understand how you're going to get rid of the docks, bindweed and nettles