Indeed it looks like the Labour rank and file is intentionally doing to its own Party what Labour did to the Liberals a century ago.

Historians please weigh in: Is there any evidence that the Whigs also volunteered in their own destruction?

It did. The situation in the 1850s was actually very similar (party-wise) to now. The Whigs fell apart over slavery; the Northern anti-slavery wing blocked the nomination of incumbent Millard Fillmore. Northern Whigs rallied to the newly-created Republican party (with an anti-slavery platform), while what was left of the Southern Whigs formed the Know-Nothing party (with an anti-immigration platform). The Know-Nothings ran Millard Fillmore again as their candidate in 1856, then joined with Southern Democrats who were against secession to form the Constitutional Union party in 1860.

The Democrats themselves fell apart in 1860, splitting into Northern and Southern Democrats (running Douglas and Breckinridge, respectively). The split in the Democratic vote meant that Douglas (who was the second-highest popular vote getter) got the electoral votes of only one state, Missouri. This in turn meant that Abraham Lincoln, who wasn't even on the ballot in most Southern states, was able to carry the election, despite a popular vote count < 40% and net favorability ratings that were probably lower than Trump. This led directly to the Civil War.