In its latest quarterly data published today (February 15), the Fos said it recorded 41,303 complaints between October and December last year, up from 35,342 complaints during the same period in 2021.
On a quarterly basis, complaints were also up 2,833 from July to September 2022.
The top five most complained about products were largely consistent with recent quarters.
Elsewhere the data showed a quarterly increase in the number of complaints relating to first charge residential mortgages, up 285 to 1,584 for the period with an uphold rate of 28 per cent.
More generally, complaints had an uphold rate of 35 per cent for the period.
Back in September, the Fos warned that an increase in the number of complaints made to it may be likely given the worsening economic environment and the rising cost of living.
New Sipp cases received by the Fos spiked at the end of 2021, up 73 per cent over just two quarters, but Sipp related cases appear to be on the decline with 433 new Sipp related complaints made in Q3 2022.
This was down from 470 the previous quarter.