Advisers have been urged to review cases where they arranged the transfer of non-protected pension rights after a portion of a client's pension went missing for four years.
Intelligent Pensions said Aviva misplaced the protected rights portion of a client's SIPP in 2008, and added the mistake only came to light because of its record keeping and provision of on-going advice.
The retirement specialist said the problem is now on the way to being resolved.
In 2008, Intelligent Pensions requested the transfer of the non-protected rights within an Aviva plan for one of its supporting advisers' clients.
At the time it was not possible to transfer protected rights to a self-invested personal pension (SIPP), and so was left invested with Aviva.
Following the abolition of protected rights and a client review meeting, it was agreed that the former protected rights fund should now be considered for transfer.
Intelligent Pensions wrote to Aviva in May to request policy information, however, the insurer wrote back to say the money had already been transferred. This did not correspond with Intelligent Pensions' records.
Following two further letters and a phone call, Aviva eventually contacted Intelligent Pensions on 14 June to confirm they had traced the pension fund.
It explained that the policy had accidentally been surrendered in their systems following the non-protected rights transfer and informed Intelligent Pensions that it would take about 20 working days to resurrect the client's policy.
David Trenner, technical director at Intelligent Pensions, said: "Had our records and advice process not been as robust, the client could very well have lost their pension fund.
"Aviva told us that the client should have noticed that he was not getting annual statements, as if it was his fault and not theirs that Aviva had effectively written off his funds."
Trenner added: "Our advice to transfer only the non-protected rights policy in 2008 is unlikely to be unique and we would encourage advisers to revisit partial transfer cases, not just as a sales opportunity but also for peace of mind in case other protected rights funds have mysteriously disappeared."
Aviva said in a statement: "We fully apologise for the mistake we have made with the protected rights portion of this client's pension. Where we have made a mistake we will always look to put it right as quickly as possible, we are in the process of resolving this matter and the client's policy will be reinstated to reflect the correct fund value. They won't suffer any financial loss whatsoever."
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