Pay in for 50 years you may have but that money’s gone. State pension payments come of the country’s current funds, not some pot that’s been set aside. It’s not far off being a Universal Basic Income for those past a certain age (I realise not everyone gets the same amount for various reasons). It’s also very generous as Drone alludes to and it’s all paid alongside whatever other pensions and income you may have. At best it’ll be means tested by the time I get there in a few decades or so.
The original function was simply to provide older people with some basic funds whilst they sorted out their affairs before quietly shuffling off to the next life. It’s morphed into something unrecognisable compared to its origins.