Complaints made against nationalised banks have risen by a third in just six months.
The Royal Bank of Scotland and Lloyds Banking Group have both come under fire for overcharging, hiking up credit card rates and mis-selling insurance policies.
If found in breach of rules governing the fair treatment of customers, the banks could be forced to pay millions in fines and compensation.
The figures from the independent Financial Ombudsman Service show there were more than 17,000 complaints about Lloyds and Bank of Scotland, whilst RBS received almost five-and-a-half thousand. Both companies received large bail-outs from the taxpayer during last year's financial crisis.
A spokesman for the ombudsman said that they have concerns about the way the companies were handling complaints and that they "need to take their customers' concerns seriously."
Tags: complaints on banks increasing