Walter Briscoe wrote:

Your memory of history differs from mine.
ISTR Mrs Thatcher's government eliminated the GLC and ILEA. At the time, I
thought that adding another ring of buroughs to London could have served
her purpose, permanently gerrymandered London and be justified from a
transport perspective.

Some of the boroughs such as Watford and Epsom & Ewell had fought hard
campaigns against being added to the Greater London area in the 1960s and
would probably have done so again. But more generally the problem was that
the GLC did not deliver that high a proportion of services, especially to
the outer boroughs, with the result that politicians in the latter were
demanding its abolition regardless of which party was in County Hall. Adding
another ring of boroughs would have been very awkward, and also have had
knock-one effects on the surrounding county councils (and the division of
services in the counties was substantially different from London so this
would also have meant the boroughs taking on additional duties that weren't
always suitable for borough/district level.) It is ahistorical to see the
abolition of the GLC as being all about Thatcher trying to shut Livingstone
up.