A Jersey accountant is restarting his legal battle to find out if he is the late Princess Margaret's secret illegitimate son.
Robert Brown, 57, said he was prepared to spend up to £100,000 fighting for access to sensitive documents relating to the will of Queen Elizabeth's sister.
He has appointed solicitors to obtain secret court papers, known as a practice direction, about the sealing of royal wills drawn up around the time of Margaret's death in 2002.
Brown believes he was born to Princess Margaret in 1955 and his father was possibly Scottish aristocrat Robin Douglas-Home, who died in 1968. He claims the later stages of her pregnancy were covered up using body doubles and that he was sent to Kenya to be brought up as the child of Cynthia and Douglas Brown in Nairobi.
He believes the documents will show how Buckingham Palace, the attorney general and a senior judge acted together to maintain secrecy around Princess Margaret's will, which he hopes includes his birth details.
Brown's case has been dismissed by lawyers for the royal family in a previous court hearing as that of "a fantasist seeking to feed his private obsession". A spokesman for the queen said: "Buckingham Palace does not comment on the allegations made by Mr Brown".
But Brown insists he has the right to find out if the royal is his mother and has appointed law firm Christian Khan, which claims a reputation for "acting in political cases where individuals bring or defend proceedings against larger organisations, including the state".
Records show Brown was born on 5 January 1955 in Nairobi, Kenya, but his birth was not registered until 2 February. He believes it is significant that a privy council meeting was held on the day he was born.
Brown's parents are registered as Cynthia and Douglas Brown, both now dead, and he claims Cynthia modelled for Hardy Amies, a favoured designer of the princess.
Aside from finding out if he is royal and whether he is due any bequest, Brown said there was an issue of constitutional significance at stake in his battle to obtain the practice direction: "The separation and independence of the judiciary from the crown and legislature, in that the practice direction was created in utter secrecy by discussion between Her Majesty, the palace, Farrer & Co [the Queen's lawyers], the attorney general and senior judges including the then head of the family division."
He said: "It is constitutionally inappropriate for the palace and private lawyers with the assistance of the attorney general to enter into utterly secret formal arrangements, to reflect Her Majesty's wishes, with senior judges."
Brown went to the high court to seek disclosure of the will in 2006 and 2007 when Sir Mark Porter, president of the family division, said it was an "imaginary and baseless claim". Appearing for Brown in the case, Geoffrey Robertson QC told the court he was "a perfectly rational man who seeks peace of mind". He lost the case, but Brown is now fighting under freedom of information laws.
His decision to appeal against the refusal of an information tribunal judge to release the papers comes as the royal family and the government battle on several fronts to resist efforts to find out more about their dealings.
Last month, Dominic Grieve, the attorney general, issued a veto that puts an absolute block on the publication of 27 letters between Prince Charles and ministers. Grieve said the letters contained the "particularly frank" and "most deeply held personal views and beliefs".
In September, the Cabinet Office launched a legal challenge to a ruling which warned that the government could be in contempt of court if it did not publish government guidance on a process which instructs civil servants to seek the approval of Prince Charles and the Queen over some new laws.
"I can understand people are sceptical because it seems to be childhood fantasy stuff, but it is not like that with me," Brown said.
Asked what he would feel if it were proved he were part of the royal family, he said: "It would be nice to be recognised as a human being of equal value."