Any wedding is a tough task to organise but the April nuptials of Prince Charles and Camilla Parker Bowles are proving to be a larger headache than normal for his mother, Queen Elizabeth II.

The courting divorcees had to scrap an initial plan to tie the knot at Windsor Castle, one of the queen's official residences just outside London, after it was discovered that the venue had no licence to hold a civil ceremony.

Licensing the palace for a civil wedding was deemed to be too much trouble -- it would have also made the venue "regularly available", for three years, to other British couples who want to marry there -- so the pair opted for Windsor's much smaller town hall down the road.

The new venue, the Guildhall, is a handsome late 17th-century building in the centre of Windsor, which will offer royal-watchers the chance to glimpse the couple before and after they say their vows on April 8 -- wrecking any hopes of keeping the marriage a totally private affair.

In addition, 56-year-old Charles will likely have to rethink his wedding invitation list, which was reported to comprise of some 700 names, as the largest room in the Guildhall can only hold 100 people.

He also may have to welcome mere commoners after his office acknowledged that the event must be open to the public free of charge.

"Yes, that is our understanding, that according to the law, members of the public will have to be allowed to the civil ceremony," said a spokeswoman at Clarence House, the heir to the throne's London residence.

But she told AFP Monday, "there are a lot of security implications with this wedding."

The family's security staff are unlikely to allow strangers to witness the royal spectacle and a decision on the matter will be taken at a later date.

Meanwhile, questions over the fundamental legality of the wedding between Britain's heir to the throne and his former mistress, 57, continue to dog the duo.

Parker Bowles may already be wearing a sparkling diamond engagement ring and have selected the designers who will make her wedding outfit, but Stephen Cretney, a legal expert, argues that only a religious marriage would be legal.

This, however, is impossible according to Church of England law as the pair are both divorced.

But Lord Chancellor Charles Falconer, the top judicial authority in the cabinet, dismissed such fears. "I remain confident that the prince and Mrs Parker Bowles can marry in a civil ceremony," he said.

"We have considered every aspect of this and taken all the appropriate advice," he told the weekly Mail on Sunday.

The 1949 Marriage Act, which updated the law on civil marriage, did not exclude the royal family as an earlier act in 1836 had done, he explained.

Other experts, however, disagree with his interpretation and argue that only a new bill introduced by the government of Prime Minister Tony Blair would gives royals the authority to wed in civil ceremonies in England.

As another alternative, some experts have suggested that they do the deed in Scotland.

Queen Elizabeth II has already reportedly expressed her irritation that the future king of England must marry like anyone else in a town hall. For her it is a sign that "the last vestige of the mystery of the monarchy will be smashed forever," a source close to the family told the tabloid Sun.