Re: Pedant Alert
"The sections of the A1 called 'A1(M)' are of sufficiently motorway-like character that the law treats them as motorways (e.g. no stopping, no bicycles, no L plates except HGVs, etc.)"
Roads with the designation Ax(M) are not only *treated* as Motorways, they *are* Motorways. Virtually the only thing that makes a Motorway a Motorway is its classification as such, which mostly relates to the restrictions you point out (no stopping, no bicycles, no pedestrians etc). The Motorway designation does not guarantee any standard of construction. There are plenty of Motorways with no hard shoulders (not even "smart" ones), single lanes, single carriageways, entry/exits on the right, traffic lights, roundabouts etc.
In my original Pedant post, I when I was talking of "A" roads that some thought of as Motorway but weren't, I was thinking of roads like the A3 [not A3(M)] which in places has long stretches of three lanes each way plus hard shoulders and central reservation with barrier but is most definitely not classified as a Motorway.
The Ax(M) designation is typically used when an Ax road is partially upgraded to Motorway over part of its distance, particularly when there is already a separate Mx Motorway with the same number. For example, there is the A3(M) which is a section of the A3, upgraded to Motorway, not to be confused with the M3, which is a completely separate road. Similarly for the A1/A1(M) not to be confused with the M1. Its a mess which has reached its zenith (or perhaps nadir) with the M74/A74(M). Although most people call this the M74, in fact much of its length from Carlisle to somewhere south of Glasgow is actually the A74(M). You can see this on many signs. During the 80s and 90s the old A74 over this section was upgraded from A74 to A74(M) in inline sections until the whole route was done. It has retained this designation despite there being no inline or separate A74 road.
I should get out more.