Complaints about Self-invested personal pensions (Sipps) have spiked in the first quarter of this year and almost doubled in numbers in the past 12 months.
Figures published this morning (22 August) showed Sipp claims were the twelfth most complained-about product, with 922 new complaints, which was a significant increase on the 521 complaints received in the same period last year.
It is also equivalent to 45 per cent of the 2,051 complaints received within the entirety of 2017/18, in just the first three months of this year (April to June).
Sipps were also one of the products which the highest uphold-rate, with 59 per cent of complaints being upheld, beaten only by instalment loans, which saw 60 per cent of complaints upheld.
Overall, in the first quarter of 2018/19 the Fos received 107,827 new complaints, with payment protection insurance accounting for 55,223 of these.
Payday loans were the second most complained-about product, with 10,979 new complaints.
The chief ombudsman, meanwhile, criticised banks for pinning the blame on their customers when they fall victim to scams.
Caroline Wayman, chief executive of the Financial Ombudsman Service, said banks often say their customers have acted with "gross negligence" in falling for a scam, which means the bank is not liable for the money which has been lost.
She said criminals' methods had evolved to such an extent - through technology and manipulative "social engineering"- that companies in the financial services sector should not assume a client is to blame for losing their money to a scammer.
In the most recent financial year, the Fos received more than 8,500 fraud and scam complaints, which was a 17 per cent increase on the previous year.
Ms Wayman said: "Each year we see more than 8,000 cases involving fraud and scams – everything from disputed cash withdrawals and identity theft, through to mobile phone Sim-swaps and fake banking websites. And where criminals are involved, both banks and their customers often tell us in strong terms that they haven’t done anything wrong.
"But it’s not fair to automatically call a customer grossly negligent simply because they’ve fallen for a scam. That’s especially true in light of the sophisticated way criminals exploit banks’ security systems – and convince customers that their money is at risk."
She added: "We often remind banks that they need to support what they’re saying with facts. And if they can’t do that, it’s likely we’ll tell them to cover the money their customer has lost."
In its latest edition of Ombudsman News, the Fos said it was a "very high bar" for a financial services company to prove one of their clients acted with gross negligence.
This is because the Financial Conduct Authority interprets gross negligence to be a higher standard than the standard of negligence under common law, with the customer needing to have shown a "very significant degree of carelessness".