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* Apparently, enough to cover the M1 from London to Birmingham to a
height of several feet, which some people thought was a good suggestion.

That'd be a different M1 from the one that doesn't go to Birmingham, then?
;-)

It has puzzled me for years that the M1 was described in early days as the
London to Birmingham motorway. Perhaps it's really the M6 and the M1 leaves
it at Rugby.

The southern end of the M6 was a relatively late addition (late
60s/early 70s?). Prior to that the London/Birmingham route was
M1/M45/A45.

--
Roger Chapman