He is particularly notable for his activities in England and for launching a successful criminal prosecution against John Henry Newman, who made accusations about Achilli's past, for libel.

On 16 June 1841, the Roman Inquisition finally lost patience and permanently suspended Achilli from the cure of souls, sentencing him to three years' penance at a remote monastery at San Nazzaro.

However, in 1842, Achilli made his way to Corfu, then a British protectorate, and claimed political asylum alleging that he was a cavaliere and that he had escaped from the fortress at Ancona.

The local authorities were minded to grant the papal consul's request for extradition until they discovered that Achilli was claiming to have converted to Protestantism and was engaged in fervent anti-Catholic propaganda, largely under the influence of Isaac Lowndes, the Scottish Presbyterian secretary of the Bible Society.

There, the committee of the Protestant College of St Julian's, Malta, appointed him professor with a special mission to spread Protestantism in Italy.

Though French president Louis Napoleon had requested that the Pope grant an amnesty, Achilli was arrested by the Cardinal Vicar and imprisoned by the Inquisition, in the Castel Sant'Angelo, for preaching against the Catholic religion and taking part in revolutionary agitation.

A series of antagonistic pamphlets established itself between Eardley and prominent English Catholic Cardinal Wiseman,[7] by turns defending and attacking Achilli.

John Henry Newman was minded to repeat Wiseman's allegations, of sexual immorality and that Achilli had misrepresented his expulsion from the Catholic Church, in a lecture but first took legal advice, on 16 July, from his confidant James Hope-Scott for fear of a libel suit.

This enabled him to bring criminal proceedings for the common law offence of defamatory libel against Newman, rather than a simple civil action for damages.

Newman was supported by a formidable team of lawyers led by Sir Alexander Cockburn and including sympathetic Anglo-Catholic Edward Lowth Badeley.

[5] Judge John Taylor Coleridge later wrote to Keble:It is a very painful matter for us who must hail this libel as false, believing it is in great part true—or at least that it may be.

[12]A leading article in The Times summarised liberal opinion when it described the proceedings as: ... indecorous in their nature, unsatisfactory in their result, and little calculated to increase the respect of the people for the administration of justice or the estimation by foreign nations of the English name and character.