Originally Posted by Polwart
What you describe is in effect the interest from a standard bank account... ...i.e, you still have a £600k asset sitting there too.
But maybe you don't. Particular types of pension investment are plans where your fund grows but access to the capital is not available. It must be used to buy an annuity to provide your pension. However, 25% of the fund can be taken as a tax free lump. As Peterb said, currently the annuity will provide less income than can be got from interest on a bank account. However, again, the contributions to this type of fund will have been tax free or limited taxed or a bit of both, depending when contributions started, so the fund will be larger than it would be had you just saved it in a bank account. But if it was savings, you would still have the capital. Payment from the annuity will depend on the payment option you choose to take at retirement, ie. simplisticly, long term = low payments and short term = higher payments.
Apologies for this bit but, on a less pleasant note, should you die before starting your annuity, the fund, less tax, will be payable to your wife. I'd need to check the tax position but I seem to remember it is a fairly high rate. Should you be unfortunate and become seriously ill and your death is imminent within 12 months, it is possible for the whole sum to be paid to you tax free. I'll leave you to work out the implications of timing a claim to your and your wife's advantage.
Think about what you feel you may need; access to funds or steady income or a bit of both. Will you fall heir to something, a parent's house for example. Remember you'll also get your state pension and a few perks which may take a little financial pressure off in time. Probability may need to be considered; is your family particularly long lived? Do you weigh 20 stone and smoke? etc.