While based in London, Malatesta made clandestine trips to France, Switzerland and Italy and went on a lecture tour of Spain with Fernando Tarrida del Mármol. During this time, he wrote several important pamphlets, including "L'Anarchia". Malatesta then took part in the International Anarchist Congress of Amsterdam (1907), where he debated in particular with Pierre Monatte on the relation between anarchism and syndicalism or trade unionism. The latter thought that syndicalism was revolutionary and would create the conditions of a social revolution, while Malatesta considered that syndicalism by itself was not sufficient. (see on Labor Unions, below). In 1912, Malatesta appeared in Bow Street Police Court on a criminal libel (defamation) charge which resulted in a three-month prison sentence and his recommendation for deportation. This order was quashed following campaigning by the radical press and demonstrations by workers organisations.