I think they run from Hammersmith to Edgware Road via the circle, then back the other way. I will be down in London (hopefully) later in the week, so I shall report back when I know more. I only realised when I looked at the tube map the other day.
[FGZ] It is never worth it. I bought a TV (using my online trade account) to be delivered to my son. I was offered "Next Day" at £12.99 but went for the free option. It was delivered the next day.