In reply to Double Knee Bar:
In actuality it was a case of putting socks over their 'rubbers' as the precursor to EB's were called and these might simply be gym pumps.
The likes of Joe Brown would put socks over their boots and supposedly this gave a better contact on wet rock. Just imagine it!
There is a story in the Villain by Jim Perrin of Brown undoing his boots on a dodgy lead, removing the boots and socks, putting the boots back on and then the socks over the boots in order to carry on. All on 1950' gear.