JAG Griffith, The Politics of the Judiciary (Fontana Press, 5th edn, 1997), Chapter 5 –

please note that this predates the Human Rights Act

HM Government, ‘Police and Criminal Evidence Act 1984 (PACE) Codes of Practice, https://www.gov.uk/guidance/police-and-criminal-evidence-act-1984-pace-codes-of-practice

David Mead, ‘The Right to Protest Contained by Strasbourg: An Analysis of Austin v UK & the Constitutional Pluralist Issues it throws up’ (UK Constitutional Law Association, 16 March 2012), https://ukconstitutionallaw.org/2012/03/16/david-mead-the-right-to-protest-contained-by-strasbourg-an-analysis-of-austin-v-uk-the-constitutional-pluralist-issues-it-throws-up/

The Government’s Ministry of Justice website has a section that explains citizens’ rights, including pages on protests and police powers: https://www.gov.uk/browse/justice/rights