The House of Lords has taken the unprecedented step of publishing a "cease and desist" letter on its website demanding that Lord Christopher Monckton, a prominent climate sceptic and the UK Independence party's head of research, should stop claiming to be a member of the upper house.

The move follows a testy interview given by Monckton to an Australian radio station earlier this month in which he repeated his long-stated belief that he is a member of the House of Lords. When asked by ABC Sydney's Adam Spencer if he was a member, he said: "Yes, but without the right to sit or vote … [The Lords] have not yet repealed by act of parliament the letters patent creating the peerage and until they do I am a member of the house, as my passport records. It says I am the Right Honourable Viscount Monckton of Brenchley. So get used to it."

The letter, sent by David Beamish, clerk of the parliaments, to Monckton last Friday and now published on the Lords' website, states: "You are not and have never been a member of the House of Lords. Your assertion that you are a member, but without the right to sit or vote, is a contradiction in terms. No one denies that you are, by virtue of your letters patent, a peer. That is an entirely separate issue to membership of the House. This is borne out by the recent judgement in Baron Mereworth v Ministry of Justice (Crown Office)."

In May, Mr Justice Lewison threw out an action at the Royal Courts of Justice brought by Baron Mereworth, who maintains that it his hereditary entitlement to attend the Lords, despite the House of Lords Act 1999 debarring all but 92 of the 650 hereditary peers, including his late father Lord Oranmore and Browne. Mr Justice Lewison ruled: "In my judgement, the reference [in the House of Lords Act 1999] to a 'member of the House of Lords' is simply a reference to the right to sit and vote in that house … In a nutshell, membership of the House of Lords means the right to sit and vote in that house."

The letter from Beamish to Monckton continues: "I must therefore again ask that you desist from claiming to be a member of the House of Lords, either directly or by implication, and also that you desist from claiming to be a member 'without the right to sit or vote'. I am publishing this letter on the parliamentary website so that anybody who wishes to check whether you are a member of the House of Lords can view this official confirmation that you are not."

The Guardian understands that the House of Lords has been consulting with its lawyers on this issue since the ABC radio interview aired. It is not yet clear what form of sanction the Lords has available to it should Monckton persist with his claim.

Last year, the then clerk of the parliaments, Michael Pownall, wrote to Monckton stressing that he was not entitled to call himself a member, nor should he use parliament's famous portcullis symbol on his letterheads or lecture slides, as he has done for a number of years.

Monckton wrote back stating that "the House of Lords Act 1999, which purported to exclude hereditary peers from membership of the House of Lords, is defective". He argued that the act removed the right to sit or vote in the upper house, but did not remove membership because peerages are granted by letters patent, which are a personal gift of the monarch. Monckton claimed in the letter that "only a specific law can annul a grant. The 1999 act was a general law."

Buckingham Palace was drawn into the dispute when it was revealed that Pownall had sought advice from the Lord Chamberlain, a key officer in the royal household, on the potential misuse of the portcullis emblem due to it being the property of the Queen. The Buckingham Palace website states that any misuse of the emblem is prohibited by the Trade Marks Act 1994, meaning Monckton could potentially be liable for fines and a six-month prison term if the palace pursues the matter and successfully prosecutes him.

Official logo of the House of Lords (left) and that used by Christopher Monckton (right). Photograph: Torsten Blackwood/AFP/Getty Images

Monckton has since been using a slightly altered portcullis emblem on his lecture slides. The two chains hanging either side of portcullis are now kinked instead of straight. It is not known whether the Lord Chamberlain is content with the change. A spokesperson told the Guardian that the palace was "aware of the issue", but it had a policy of not commenting on private correspondence between it and an individual.

Monckton is currently on a lecture tour of Australia discussing climate change. The tour has been dogged by venue cancellations after he referred to the Australian government's former climate advisor Prof Ross Garnaut as a fascist during a recent lecture in Los Angeles. Footage of the lecture also showed Monckton displaying a swastika next to one of Garnaut's quotes. Monckton later apologised for "having made the point I was trying to make in such a catastrophically stupid and offensive way".