The Solicitors Regulation Authority (SRA) has warned in-house lawyers over misrepresenting themselves to the public as independent legal advisers.

The warning notice to in-housers comes following complaints that some companies have been sending letters to debtors, purporting to be from third party-lawyers.

Last month, the Financial Conduct Authority (FCA) handed out a £2.6m fine to pay day loans company Wonga, after it was discovered to have been sending letters from fictional law firms to customers in arrears, creating the impression their debts had been passed onto a third-party agency.

Last week, senior MPs called for an investigation into the practice which has been used by a number of British banks, which send out letters headed with the names of law firms despite the letters being sent from the banks themselves.

Lloyds, The Royal Bank of Scotland and HSBC have all been found to use this practice in correspondence with debtors, while Barclays and the Student Loans Company have also received criticism for writing to debtors using the name of a subsidiary.

The SRA warning is directed at in-house solicitors, reminding them of their duties in line with the mandatory principles of the authority and its Code of Conduct.

The warning states: "Overall, these approaches appear to be attempts to give the impression to a third party that an external agency or firm has been instructed to take legal action, up to and including, court proceedings.

"Further concern has been caused by complaints of solicitors having taken unfair advantage of a third party's lack of legal knowledge, particularly in debt collecting matters, where the third party is unrepresented."

The statement refers directly to principles 2 and 6 of the code: "to act with integrity" and "behave in a way that maintains the trust the public places in you and in the provision of legal services".

SRA executive director, Richard Collins commented: "We believe attempts are being made to mislead third parties – invariably individual debtors – that their case has been referred to an independent law firm to pursue the debt, when in fact it is the in-house legal team. We believe such approaches do not meet the requirements of the Code of Conduct."

"Overall, the obligation on solicitors is to take positive steps to ensure third parties are clear about their status and relationship with the organisation seeking recovery of the debt. Failure to comply with this warning notice will lead to regulatory action."