John B wrote:

The fact that Mrs T's government was /so/ unpopular in the mid-80s
that Labour managed to control the GLC as well, and that she was so
incapable of tolerating dissent that she abolished it as a result, is
fairly irrelevant.

Which is not a "fact" as I've pointed out elsewhere; the drive to abolish
the GLC predated Ken coming to power. Also the crucial election was 1981
(and won by Labour on a moderate manifesto with a moderate leader who was
promptly deposed) and wasn't that different from 1967, 1973 or 1977 when the
incumbent Westminster government lost the GLC in a mid term election.

...and as someone has mentioned below, the Watford-type-places that
would have permanently gerrymandered London for the Tories were
themselves strongly opposed to integration, otherwise there's a good
chance it'd've happened either in the creation of the original GLC or
during the 1980s.

I don't think that would have worked. Remember the GLC was elected by first
past the post, initially multi-member borough-wide then single-member from
1973, and the Labour majorities were often substantial.

FWIW here are the seat outcomes, courtesy of
http://www.election.demon.co.uk/glc/glcresults.html

From 1964 to 1973 the GLC consisted of 100 directly elected councillors and
16 Aldermen.

1964:
Elected: Labour 64, Conservatives 36
Full Council: Labour 75, Conservatives 41

1967:
Elected: Conservatives 82, Labour 18
Full Council: Conservatives 92, Labour 24

1970:
Elected: Conservatives 65, Labour 35
Full Council: Conservatives 76, Labour 40

The election system changed to single member for the 1973 election, with the
council cut to 92 elected and the Aldermen to 15.

1973:
Elected: Labour 58, Conservatives 32, Liberals 2
Full Council: Labour 67, Conservatives 38, Liberals 2

Aldermen were abolished from the 1977 election onward.

1977:
Conservatives 64, Labour 28

1981:
Labour 50, Conservatives 41, Liberals 1

Note also the maps of results. Although there's a clear outer vs inner
pattern in the years of Conservative victories, Labour victories often
carried outer east and west parts, and turn the map into a north & south vs
centre divide.

http://www.election.demon.co.uk/glc/glcmap.html

Leaving the Aldermen to one side (as they seem to have been allocated
reasonably proportionally so just reinforce the existing proportions), I
can't really see the GLC as having gone Conservative on any realistic larger
boundaries in 1964 or 1973, and even 1981 would have been difficult as not
every additional seat would have gone Conservative. On the suggestion in
this thread that the government should have expanded the boundaries to
secure a majority in a 1985 election, leaving aside both the opposition to
being added and the existing outer boroughs demand for outrigh abolition, I
don't think it would have done the trick as it would have been just another
mid-term election.

Also the website, run by a Labour councillor, has a history of the GLC that
challenges some of the myths about abolition:

http://www.election.demon.co.uk/glc/glccomment.html