Given recent events, thought this might be of use. Feel free to add other resources.
Your rights if arrested:
www.gov.uk/arrested-your-rights
In Scotland:
www.citizensadvice.org.uk/scotland/law-and-courts/legal-system-s/police-s/if-you-are-arrested-and-held-in-custody-by-the-police-in-scotland/
Arrested at a protest? Your rights:
www.libertyhumanrights.org.uk/advice_information/what-if-im-arrested-at-a-protest/
Organisations that may be able to help:
sex-matters.org/
www.faircop.org.uk/contact/
freespeechunion.org/
It might be useful to carry a printout/ card with details of a knowledgeable gc lawyer? If anyone can suggest suitable people, who are okay to be added, please do so!