The figures, which cover the first half of 2019, show that Al Rayan Bank attracted 50.7 complaints for every 1,000 customers, while Barclays racked up 28.9 complaints.
However, a host of inactive lenders also feature in the FCA data. Blemain for example was the most complained about of all, attracting 55 complaints for every 1,000 customers, while Bradford & Bingley (49.8), NRAM (35.1) and Standard Life all rank towards the top of the home finance category.
A spokesperson for Al Rayan said: “While our complaints relating to home finance have reduced, we acknowledge that there is more to do. The bank has committed to a significant investment in all stages of the customer journey and we’re confident that this will see home finance complaints continue to decrease.”
Barclays have been contacted for comment.
In terms of upheld complaints, Legal & General Partnerships saw more than three quarters (76.8 per cent) of complaints against the firm upheld by the regulator.
It was followed by a raft of high street lenders, led by Coventry Building Society at 74.4 per cent, ahead of Barclays (72.2 per cent),TSB (70.5 per cent) and HSBC (70 per cent).
The FCA separates out complaints involving intermediated cases, though this remains a relatively small section of the data.
Atom Bank topped the list with 19.6 complaints per 1,000 sales, followed by London & Country (16.1) and Connells (15).
Mortgage complaints falling
The FCA data revealed that the level of complaints regarding home finance cases are heading in the right direction. For every 1,000 home finance accounts held, there were 8.7 complaints. This is down from 9.6 in the last half of 2018 and 9.8 in the first half of last year.
While the overall number of complaints rose to 4.29 million from the 3.91 million in the second half of 2018, this was largely driven by a 34 per cent increase in the number of complaints related to payment protection insurance (PPI).
In total, the product accounted for 49 per cent of all complaints received, and when excluded complaints numbers actually fell six per cent in the six months.
After PPI, the most complained about product remains current accounts, which make up 14 per cent of reported complaints. This is followed by credit cards at eight per cent and motor insurance at six per cent.