If you die before taking benefits from a pension, the full fund value is normally paid to the estate as a lump sum, free of tax. It is possible to give guidance to the pension trustees about your beneficiary by completing a nomination form. In doing so, you are able to identify the name of the beneficiary and their share of the fund. The payment will not normally be provided tax-free to the beneficiary.
If death occurs while drawing your pension, then any death benefit would be determined by the terms of the annuity that was purchased at retirement.
If your nephew is not a dependant, then you will have to buy an annuity with a 10-year guarantee built into it. Widely available, it would pay the equivalent of the unpaid income in a lump sum in the event of your death to a nominated person. They tend to cost 5% of the income, but it's a price people are often happy to pay.