For a fair part of the 80s and 90s, workers could "contract out" of SERPS at no cost to themselves at all. They'd have exactly the same deductions from wages, but some of it was diverted into a personal pension scheme instead of going to the government. As mentioned upthread, so peoples "contracted out" private pension schemes are now worth around £100k, and given the changes in state pension rules over the last few decades, those people are still eligible for full state pension too! So basically £100k that cost them zilch, nada, nothing.
Even paying in small extra amounts to a company pension scheme often meant employers would match it or even more, so an employee paying in just a tenner a month may find the employer also paying in a tenner, or more, so maybe £25 per month in total going in, month after month, year after year, decade after decade. You're soon up to a pension pot of tens of thousands with compound investment growth.
Fair enough that the smallest of employers tended not to have pension schemes, but lots of major employers of low earners certainly did - such as supermarkets, factories, etc., as well as most of the public sector. Perhaps those working places with no such scheme (and usually no other perks either), should have thought about changing employers?
As said above, I hope all the media attention re waspis, state pension age increasing, poverty in old age, WFA removal, etc., makes younger people think and make themselves more aware of the importance of planning for their own old age and retirement.