Rules about the disclosure of royal lobbying must change, campaigners have said today - whichever way the Surpreme Court rules on Thursday.

The call comes ahead of the Surpreme Court decision in which the Guardian newspaper will be told if Prince Charles's letters to ministers will be disclosed.

The rules were changed in 2010 so that any new request for the disclosure of royal letters would fall at the first hurdle.

Campaign group Republic has called for a root and branch review of royal secrecy, branding the monarchy one of the country's 'most secretive institutions'.

Republic's CEO Graham Smith said today:

"Charles is a growing threat to Britain's democracy - clearly he is keen to exert real power and influence over the political process."

"This makes it all the more urgent that royal secrecy comes to an end - there is no justification for giving the royals such extraordinary protection from scrutiny."

"The former Attorney General claimed it was necessary to continue to pretend Charles is impartial.  It is in fact vital we show that he is not."

"Even if the court finds in favour of disclosing these ten-year-old letters, the law now makes any further disclosures impossible.  That has to change."

"The monarchy thrives in a culture of official secrecy and excuses that cannot be justified.  In a democracy the voters must know what the royals are up to and how they are abusing their position and privileges."

"Charles clearly has his own political agenda - yet his name won't be on the ballot in May.  So we all need to know what influence he is trying to exert and what impact he is having on policy."

Republic has recently launched a Royal Secrets campaign, calling for an end to all royal secrecy.  Details are at