Camberwell Fair, held where the Green is now situated, was a source of conflict between the authorities and fair-goers until it was eventually suppressed completely. In 1827 there were riotous scenes as the police intervened to prevent a preacher addressing a crowd on Camberwell Green. Exactly what his message was, and why the local magistrates wanted to stop him, is unclear from the following account published in The Times, 21 August 1827.
'Riot at Camberwell
On Sunday, at two o'clock, according to previous announcement, Mr Smith, of Penzance, arrived on the ground where Camberwell fair is held, in a hackney coach, attended by an immense number of persons who had followed the vehicle all the way from town. The moment he alighted, a constable stepped up and told him that the Magistrates had given directions that he should not be permitted to hold forth on the Green. On receiving this notification Mr Smith demanded the names of the Justices who had issued such a mandate and upon being informed, he proceeded to take down their names in his note-book. He then called for a chair, intimating to the mass of people by whom he was surrounded that as soon as he was furnished with an article that would elevate him a little above the rest, so as to he heard by all his auditors, he should then explain to them the chief causes of the opposition manifested by the Magistrates against him. Having waited for some time, during which the shouts of the crowd were deafening, a parson was seen making his way towards the preacher holding up a chair; and having placed it down, the later was about to ascend when two or three constables approached and again reiterated their directions; but no sooner had they spoken than they were attacked by the mob, who were determined that Mr Smith should be heard.
A reinforcement of police, however, having come to the assistance of the constables, a general row took place, during which broken heads were given on each side, and in the midst of the affray Smith, like a skillful General, made a hasty retreat, and escaped, leaving one if his chief supporters, a man named Perring, in custody. In appeared Smith proceeded afterwards into the parish of Lambeth, followed by a crowd of ragamuffins, and having ascended the steps of a new building in Surrey New-road, he there harangued the motley crew, exclaiming most vehemently against the magistrates, and declaring that their names and conduct towards him should be published and go forth to the world.
The neighbourhood of Camberwell was a scene of noise and confusion the whole of the day; the mob, amongst whom were numbers of pickpockets, expecting the return of the preacher. Yesterday morning, Perring, who had been apprehended the day before, was taken before the magistrates and held to bail for assaulting the officers in the execution of their duty. He was anxious to address the magistrates on the subject of Mr Smith's visit to Camberwell, but the magistrates declined hearing anything, conceiving that Mr Smith's efforts were calculated to do much more harm than good at the fair'.
I am guessing that 'Mr Smith of Penzance' is George Charles Smith (1782–1863), known as ‘Boatswain Smith'. Originally from London - he was apprentice to a bookseller in Tooley Street - he was press ganged into the Navy before becoming pastor of a baptist chapel in Penzance. In 1817 he spread his activities to London, preaching in particular to sailors, river and canal workers. He opened a floating chapel in the Thames and established charities including the the Shipwrecked and Distressed Sailors' Family Fund. The practice of open air non-conformist preaching was initially met with official opposition, though it later became common-place.