Afraid you are wrong there sft. If a road carries the suffix (M) it is a motorway with all the various extra rules etc. The reason a motorway has the suffix is that it substantially follows the route of an old A road ie it has been upgraded. To use the example in question, the A74 from Gretna to Abington was basically an upgrade of the , then, existing A74 dual carriageway. The section from Abington up to the Hamilton area was a completely new road which took over from the old single carriageway road and is thus deemed to be a new route, so does not need the suffix. I agree it would be easier to just call the whole thing the M74, but some bloke in Whitehall would probably lose his job if he didn't have to make these ludicrous red tape decisions!!