Campaigners will be writing to the Metropolitan Police to ask why they failed to speak to King Charles after he was reported on suspicion of breaking cash-for-honours laws.

Following reports in the Sunday Times it is alleged that an honour was offered to Saudi billionaire Mahfouz Marei Mubarak bin Mahfouz, in exchange for donations.

The police have announced that they have sent files to the Crown Prosecution Service, but have only spoken to two men, one in his 50s and another in his 40s.

Speaking for campaign group Republic, Graham Smith, who reported Charles and his aide Michael Fawcett to the police, said today:

"There is a clear public interest in knowing that the police have dealt with this case, and with Charles, just as they would anyone else. They must act without fear or favour and they cannot allow Charles to think he's above the law."

"We now have a head of state who has been accused of exchanging honours for donations to his charities, which if true is a clear breach of the law."

"It is inconceivable that Michael Fawcett could make any such promises without the knowledge and involvement of Charles, who would be the one recommending honours to the government."

"Charles knew Saudi Mahfouz was making donations to one of the charities he had set up, and he personally awarded the honour. At the very least this raises the need for the police to question Charles under caution."

"We cannot tolerate a situation in which our head of state is above the law. That is a direct attack on the fundamental principle that the law applies to everyone equally regardless of status or rank."

"We will be writing to the police to seek an explanation."