The Financial Ombudsman Service has ramped up efforts to shield itself from data requests over concerns people are using pseudonyms to hide their real name and "place a burden" on the service.
The Fos is particularly concerned fake names are being used on whatdotheyknow.com, a website designed to help the public make freedom of information requests under the Freedom of Information Act 2000.
The Fos is now asking for proof of identity and address before responding to what it deems are suspicious freedom of information requests.
In some cases the ombudsman is requesting either a passport, driving licence or national identity card and a mortgage statement, utility bill, council bill or bank statement before responding to requests.
Proof of identity was required in response to one request on the site where an individual had used a first initial and his surname.
The request asked for statistics on how many cases were concluded by investigation without adjudication, adjudicator without final decision, and ombudsman with final decision in the first three months of 2019.
The Fos said: "We have concerns that individuals are using pseudonyms on the ‘What Do They Know’ website in order to hide their real name and place a burden on the ombudsman service.
"This is not using the Freedom of Information Act 2000 with the spirit it was intended, so because of this, we consider it necessary to seek your identity before responding to any further requests for information in line with section 8(1)(b) of the Act."
Guidance from the Information Commissioner’s Office, the body which governs information rights in the UK, states any variation of an individual’s title or first name combined with their surname is enough to qualify as a real name, including an initial and surname.
The ICO warns that a request submitted under a pseudonym will be invalid, but also said if the name is not an obvious pseudonym and the public authority has no reason to believe one is being used then the authority should "just accept the name provided at face value".
The ICO said: "Whilst this may mean that some pseudonymous requests will slip through the net, we would not want to see a situation where authorities routinely carry out checks on requesters’ identities.
"The Act provides a public right to information, not a right limited to certain individuals."
The ombudsman did not comment any further on its reasoning for requiring proof of identity, or whether it had detected any prank cases.
Phil Castle, managing director at Financial Escape, said: "I am all for transparency. If you want to ask difficult questions, for example an FOI, then you need to be prepared to put your head above the parapet and take any flak that then returns your way.
"The Fos asking for this are right to do so as we don’t want their time and our money wasted on frivolities, but valid questions need to be asked and answered."