David Boothroyd wrote
[...]
Never mind that, what about the introduction of criminal offences
which were summarily triable only? That was some time in the 1980s;
before then, a defendant could insist on a jury trial for literally
anything.

Nope, summary only and/or no defendant's option offences from 1879 or
before I understand.

The general rule from 1952 was all offenses with a maximum sentence of
three months imprisonment or less (with lots of exceptions).

Think Assault or no TV license.

My reference says the Criminal Law Act 1977 reduced the number of
categories from five to three, so as with the other examples of modern
legal degeneration it's far older than you think.

--
Mike D