in September we will be driving from The Lakes District to The Cotswolds on the M6. Allowing for one stop along the way, what would be the one site-location we should not miss or enjoy a good lunch?
if it was me I'd visit Ironbridge
Yup. Ironbridge should be your stop. You won't regret it.
3 votes for Ironbridge.
Or anywhere in Cheshire (except Crewe) for a bite in the beautiful countryside, or many places in rural Staffordshire, maybe Penkridge.
Or you could stop in industrial Staffordshire around the Potteries, ie Stoke on Trent. But expect industrial, and maybe a tour around Wedgwood.