Such annuities are calculated on the expected yield from the initial investment and the annuitant's life expectancy to project the probable payment period. Payments are deemed to be part capital and part interest and tax is payable only on the interest content.
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Not on a "force purchase" retirement fund annuity
The capital part is also taxed as you draw it, because the money got tax relief on the way in.
It is only capital purchase annuities that are treated the way you describe
tim