Alan Wright, 75, was once a Grand Master in the secretive organisation and would have been present at meetings attended by Prince Michael of Kent.
He resigned when the details of his activities came to light.
Now he could face jail when he appears at Ipswich Crown Court for sentence next month. The maximum term for incitement is 10 years. Suffolk Police set up the sting after gathering intelligence on Wright’s private life, with specialist officers pretending to be a child online.
Wright thought he was communicating with a 14-year-old boy and sent him pictures of his private parts over the internet. Through gay dating app Grindr he arranged to meet the “boy” at Bury St Edmunds railway station, Suffolk, last November.
However, when Wright arrived he was met by officers who took him to a local police station for questioning. A former Grand Master of the Grand Council of Royal and Select Masters, he was also Grand Master of the Provincial Grand Lodge of Mark Master Masons of Essex.
Wright regularly attended meetings at a Freemasons hall in St James Street, London, and has been described as a “significant” figure in the organisation. Sources say that he would have attended some meetings with Prince Michael, who is a popular Freemason, but the men were not friends.
A spokesman for the United Grand Lodge of England said: “We were made aware of an allegation against a Freemason on December 1, 2016, who immediately resigned from the organisation.
“Having learned of the situation we have no further information currently, and fully believe that this is a one-off, isolated incident.
“We can confirm that we will fully assist the police and relevant authorities if we are approached or if we know of any way that we can voluntarily do so. No such request has been made.
“United Grand Lodge of England places great importance on total transparency in its dealings with members and we have a robust disciplinary system to deal with members who break the law, break our rules or conduct themselves in a way which would bring Freemasonry into disrepute.
“Criminal activity is completely unacceptable within the organisation and totally alien to our values.”
Wright was not at his home in Little Downham, near Ely, Cambridgeshire, to comment.