Lay 'em on 100mm of concrete - I thought there was a drawing somewhere on the site for a flagged driveway, but it's not where I thought it was. I'll dig out one of my old cross-section in t'morning and post it some time tomorrow.
i can't be bopthered with the concrete route as i am above a gas pipe and if they ever needed access then the full lot will be ripped up. At least if slabs they can lift certain slabs and remove the type 1 etc