Filip's research interests include theories of imperialism and the capitalist state, social movements, political thought, and British and Middle Eastern politics.

Most recently, he edited a volume of the journal Political Studies entitled: The Capitalist State in the Global System 2020+ that included his text on 'The ideal collective capitalist' in times of the pandemic.

In 2017 he obtained his habilitation for his work on theories of capitalist imperialism, which included the monograph Capitalist Imperialism in Contemporary Theoretical Approaches.

Filip gained his PhD in 2005 with a thesis entitled 'Reforms of the British trade union movement between 1964 and 1997: a political science analysis'.

He is also an activist in the teachers' trade union and in anti-war, anti-racist social movements.