Your income in retirement will be linked directly to the value of an underlying fund of investments. Generally, you can choose the types of fund, for example:
The more risky the underlying fund you choose, the more your retirement income may vary - both up and down.
Your starting income is based on an assumed growth rate (similar to the assumed bonus rate). If the fund grows at the assumed rate, your income stays the same. If growth exceeds the assumed growth rate, your income increases. If growth is less than the assumed rate, your income falls. A few unit-linked annuities let you invest in a 'protected fund' which limits the fall in your income.
Most unit-linked annuities do not guarantee any minimum income. Even if your income is based on an assumed growth rate of 0%, your income could still fall if the underlying investment fund falls.
You should not consider a unit-linked annuity unless you can cope with an income that can swing widely and may fall. You would need a large pension fund or other sources of income (or both) to fall back on. Unit-linked annuities are higher risk than either conventional or with-profits annuities.