Last year they accounted for 25% of completed investigations but this has risen to 46%. The largest increase was Self Invested Personal Pensions.

There were just over 200 complaints concerning suspected pension liberation, compared to 180 the year before.

The most common topics of completed investigations were: pension liberation (accounting for 20% of completed investigations), misquotations/misinformation and failure to provide information or act on instructions.

The figures were published in its annual report and accounts for 2015/16. The organisation reported it had stayed within budget, with costs of £3.381million.

The cost per case was £942 and cost per completed investigation was £2,584.

Overall, the service took on 1,363 new investigations, which was 6% more than in 2014/15.

It completed 1,308 investigations, 35% more than the previous year and handled around 5,000 enquiries, 18% more than in 2014/15.

Excluding all anomalies from both years, new investigations were up by 7% over 2014/15.

Around 40% of complaints determined by an Ombudsman were upheld, at least in part. Complaints determined by an Ombudsman represent 37% of all completed investigations.

The Pensions Ombudsman Service said 63% of cases were resolved informally by its adjudicators and 37% formally with an ombudsman’s decision, reversing last year’s position when 44% of cases were resolved informally and 56% formally.

Around 40% of cases formally decided by an ombudsman were upheld or partly upheld.

Investigations ended in the year took 10 months on average to complete.

The Pensions Ombudsman, Anthony Arter, said: “There has been a marked increase in the number of pension complaints coming to our office.

“This is particularly so in respect of personal pensions where in the financial year 2014/15 they accounted for 25% of our completed investigations. This has increased now to 46% with the largest increase being Self Invested Personal Pensions.

“Our priority in the past year was to find ways to deal with complaints more efficiently while at the same time simplifying the wider customer journey. Changes to our internal processes and a focus on dialogue and early resolution are helping us to deliver this. It has resulted in a dramatic increase to 63% in the number of cases resolved informally."

• Take part in our reader survey to be in with a chance of winning a £30 Amazon gift voucher. Click here to take part and enter the prize draw.