Conventional annuity rates have fallen 6.98% while enhanced rates have dropped by 5.32% since June 2009, according to figures from MGM Advantage.
Almost half the drop in conventional rates happened between June and September this year, falling by an average of 3.65% over the quarter.
The gap between the average income paid by the top and bottom quartile annuities is also growing, MGM says.
In June 2010, the difference between the highest and lowest paying annuities for men was 35.06%, which grew to 36.83% in September.
For women, the gulf grew from 34.7% to 37.22%.
Over the quarter, the difference between the average standard annuity and the average enhanced annuity was 23.94%, This is equivalent to an extra £12,490 in pension income for men with a pot of £50,000.
"The results also show the significant increase in income that an enhanced annuity can provide but not enough people are declaring the health conditions that could allow them to qualify for up to 20% more income each year," says Craig Fazzini-Jones, director at MGM Advantage.
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