At the tender age of 28, and self-employed, I started a pension fund with A***y L**e. I paid in the maximum allowable, taking into consideration back allowances. That amounted to 3 years income in one hit, followed by additional payments over the next few years.
That was 24 years ago. The fund is now worth less than the investment; not adjusted for inflation, but actual pounds sterling. My advice is that unless you have a cast iron company pension to pay in to, or a civil service one, leave well alone and concentrate on paying off your mortgage. I could (and should) have paid off my mortgage with that money. As it stands, I still owe the lender.