In the culmination of a dispute that began in 2009, the Pensions Ombudsman found Sun Life had taken too long to transfer funds to Just Retirement, who was selling an annuity to the client known as Ms Hobin.
The Association of British Insurers said 10 working days is standard fair practice for transferring funds.
Because of Sun Life’s delays, despite enquiries from the adviser and annuity provider, Ms Hobin received an annuity rate of 5.98 per cent instead of the originally-quoted 6.05 per cent.
Sun Life attributed the delays to several factors including inclement weather and being understaffed.
Ms Hobin’s adviser believes the difference in rates could amount to £238.
Ombudsman Tony King also ordered the company to pay Ms Hobin £50 to compensate her for late receipt of the balance and £100 for distress and inconvenience.
Mr King said: “Sun Life Financial say that if they had been made aware of the 21 December deadline, they would have treated the application with priority. But it is clear that on two occasions, Just Retirement did make this fact clear.
“I do not find that any additional notification of the deadline was necessary, for example to underline the importance of it being met.”
Last year, the Pensions Ombudsman ordered Sun Life to repay almost £24,000 to a client after mistakenly paying an incorrect rate.