M stands for motorway

Hey Jackie, hope you don't mind my answering your question (hope Jo doesn't mind either!) - but I just got back from a trip to the UK so can assure you, the motorways there are like our freeways here - double and sometimes triple lanes in each direction. But Jo is right - the outer lane (in their case, the right-most, in ours, the left-most) is used strictly for passing. (Let me tell you, I was well impressed - here in Canada, at least the bits of it I drive, people are bluddy rude about hanging about in the fast lane instead of passing and getting out of the way.)

What they (across the pond) call an "A road" is a single carriageway.

In fact, come to think of it, I'm not so sure we use the term "freeway" in Canada - just "highway." More frequently, "401" (our principal cross-country route), as in:

"I took the 401 to Brockville today."

Our major motorways all seem to start with the number 4 - makes sense that the 401 is the 401, since it's the first and longest (it's aka the trans-Canada highway). If you go on a smaller road, you generally refer to it by number or, if it doesn't have one (rare), by name:

"I prefer to take Highway 2 and then the Parkway if I'm going to Brockville. If I'm going to Ottawa, I'll take Highway 15, then the 417."

I'm sure y'all were just scintillated by this!
(bet you're wishing Jo had got in with an answer before me!)

If you can't see the bright side, polish the dull side.