"This is the problem, that people are led to think that they have paid in to anything - that isn’t the case at all."
There is a legitimate point that the government has entered a social contract. Workers pay the pensions of retired people and expect the same to happen when they retire.
The obvious issue that in the years the state pension started the demographic balance has skewed with far more people retired and proportionally less people working who's contributions pay for those pensions.
This is also true of government pensions like the teachers pension scheme.
This can be made cheaper by
eroding the real value of the state pension ( which the triple lock currently largely minimises this effect) or
Increasing state pension age
as PP posters have said means testing the state pension. This disincentives people to save for their own retirement ( unless very wealthy) as they lose 11k a year state pension. Millions of people might only have a 10 to 15k pa private pension to top up their state one ( or less)
It's difficult to change to a funded model now as it is unfair to ask workers to save for their own state pension whilst at the same time taxing them to pay for current state pensioners.
Means testing the benefit itself is likely political suicide as older people are far more likely to vote than younger ones...