Because that, in itself, would absolutely crash the economy. It would mean defaulting on all government bonds (Gilts), which currently pay for every pension in payment and make up around half the value of every pension fund that’s not paying out. The reason that every pension fund holds them are because they are considered “risk free”. They are effectively £1,000 notes that pay the bearer somewhere between 0.5-5% per year for their term (1-15/20 years as a rule).
I’ll tell you now, you can absolutely 100% forget that as an idea. Won’t happen, can’t happen, never going to happen. It won’t even be floated as an idea by anyone.