The Society began active propaganda for a reform of the parliamentary representation: one of its manifestoes, prepared by Frost and Thomas Hardy showed that 257 representatives of the people, a majority of the existing House of Commons, were returned by a number of voters that was less than 0.1% of the nation.
The Constitutional Society elected Frost a deputy to the convention of France in 1793, his colleague being Joel Barlow, whose expenses he paid.
Defended by Thomas Erskine, he was found guilty, and was sentenced to six months in Newgate Prison, to stand once in the pillory at Charing Cross, to find sureties, and to be struck off the roll of attorneys.
On 19 December 1793, Frost was brought out of Newgate in a state of collapse; but the crowd took the horses out of his carriage and drew him along the streets, shouting.
In December 1813 Frost received from the Prince Regent a free pardon; and on 8 February 1815, the Court of King's Bench replaced his name on the roll of attorneys, but held that he was presumably unfit for the employment.