A pension is a long-term investment not normally accessible until age 55 (57 from April 2028 unless the plan has a protected pension age). The value of your investments (and any income from them) can go down as well as up which would have an impact on the level of pension benefits available. Your pension income could also be affected by the interest rates at the time you take your benefits.
The tax implications of pension withdrawals will be based on your individual circumstances, tax legislations and regulation which are subject to change. You should seek advice to understand your options at retirement.